• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.232-237
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• 2004

Anatahan Volcano in the Commonwealth of the Northern Mariana Islands (CNMI) erupted for the first time in recorded history on 10 May 2003. The underwater acoustic records of earthquakes, explosions, and tremor produced during the eruption were recorded on a sound-channel hydrophone deployed in February 2003. Acoustic propagation models show the seismic to acoustic conversion at Anatahan is particularly efficient, aided by the slope of the seamount toward the hydrophone. The hydrophone records confirm the onset of earthquake activity at 01:53Z on 10 May, as well as the onset (at ${\~}$06:20Z) of continuous, low-frequency (5-40 Hz) acoustic energy that is likely volcanic tremor related to magma intrusion. The hydrophone recorded a total of 458 earthquakes associated with the eruption. To predict the character of acoustic signals generated from Anatahan, we developed a moment-tensor representation of a volcano-seismic source that is governed by the geometry of the source and the physical properties of the magma. A buried magmatic pipe model was adopted, and numerically modeling source parameters such as the pipe radius and magma viscosity enable us to grasp the inward nature of Anatahan Volcano.

• Economic and Environmental Geology
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• v.28 no.2
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• pp.139-145
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• 1995

Tungsten skarn mineralization of the Sangdong mine is localized in the interbedded limestone layers of the Myobong Slate Formation and in the limestone of the Pungchon Limestone Formation of Cambrian age. Fluid inclusion, gas composition and Nd-Sr isotope for granites and skarns have been investigated. Gas compositions show $CO_2$ rich in the Sangdong granite and CH, rich in the Nonggeori and Eopyeong granites. The initial $^{87}Sr/^{86}Sr$ and $^{143}Nd/^{144}Nd$ ratios of the Sangdong granites have 0.714~0.716(${\varepsilon}_{Sr}$=138~162) and 0.51173~0.51178(${\varepsilon}_{Nd}$=-14.4~15.5), respectively. And their two stage model ages range from 1687 to 1764 Ma. The granite characterized by high strontium initial ratios and negative eNd value could have originated from the old continental crust source. Low homogenization temperature of the Sangdong granite having $203{\sim}296^{\circ}C$ with 1.9~9.2 NaCl equiv. wt% indicates the post-magmatic hydrothermal alteration temperature. Skarn ore fluid responsible for tungsten mineralization has been evolved from CH, rich fluid of early pyroxene garnet skarn to $CO_2$ rich later quartz-mica skarn.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.599-612
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• 1995

Some REE ore deposits are located in the middle part the of Korean peninsula. Geotectonically, the REE ore deposits situated on the Kyemyeongsan Formation of northern margin of the Okcheon geosynclinal belt and in the transitional zone between Kyeonggi massif and the Okcheon belt, with a deep-seated fracture separating the two tectonic units. The Kyemyeongsan Formation are different in lithology and metamorphic grade from the Gyeonggi massif and the Okcheon super group. The sequence of Kyemyeongsan Formation is dominantly composed of acidic metavolcanic and volcaniclastic rocks associated with alkaline igneous rocks which are related to volcano-plutonism. The REE ore deposits contain mainly Ce-La, Ta-Nb, Y, Y-Nd and Nd-Th group minerals. More than 15 RE and REE minerals have been found in the deposits, such as allanite, fergusonite, thorite bestnaesite, euxenite, polyclase, monazite, columbite, (Nb)-rutile, okanoganite, sphene, zircon, illmenite and some other unknown minerals. According to the characteristics of the mineral association, the REE ore deposits may be divided into 4 ore types; Zircon-REE, allanite-REE, feldspar-REE and fluorite-REE type. The Sm-Nd isochron age of the REE ore is 330 Ma, and the Sm-Nd model age is 1.11 Ga with ${\varepsilon}_{Nd(t)}$ being - 2.9. This data suggest that the REE ore deposit was formed in the early Carboniferous, and the ore-forming material came from the mantle. The REE ores show distinct light REE enrichment with strong negative Eu anomaly. The REE patterns of schistose rocks from Kyemyeongsan Formation are similar to felsic volcanics from rifts or back arc basins in or near continental crust. The genesis of the REE ore deposit is quite complicated. Different geologic processes are displayed in the studied area; sedimentation, volcanic activity, metamorphism and hydrothermal replacement. Alkali granite has suffered extensive post-magmatic metasomatism of a high temperature to produce alkali metasomatites. Geochemical charateristics show that metasomatism of alkaline fluid was probably the dominant ore-forming process in Chungju district.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.293-303
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• 2002

Applying elastic plate model, we estimated elastic thickness and rigidity of the lithosphere in southern part of the Korean Peninsula($332km{\times}332km$ area of which center is $36.5^{\circ}N$ in latitude and $127.5^{\circ}E$ in longitude) by analysing terrain data and gravity data measured up to 2002. We tried to exclude the East Sea in choosing the study area because it has different tectonic environment. The mean Moho depth was estimated to be 30 km by power spectrum analysis of gravity data in the study area, Assuming one layer crust and applying elastic plate model, the loads with wavelengths of greater than 300 km are locally compensated, loads with wavelengths in the range 80-300km are partially supported by the strength of the lithosphere, and loads with wavelengths of less than 80km are almost completely supported by lithospheric strength. Assuming crustal model and rigidity, we calculated predicted coherence and compared it with observed coherence. As a result, we wert able to estimate the effective elastic thickness to be of 15 km(corresponding flexural rigidity is $3.0{\times}10^{22}Nm$). This indicates that the crust of the study area is relatively weaker than other old and stable continental regions but is similar to continental margins or oceanic area. The low rigidity could be explained by many tectonic and thermal activities such as orogenic activities, magmatic intrusions, volcanic activities, foldings, faultings, etc.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.165-181
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• 2005

The granitic rocks distributed in the southern part of the Yangsan Fault are classified into five distinct rock facies based on the field relation, petrography and geochemical characteristics. These five different rock facies can be grouped into two considering their origins. Group I, which reveals various evidences of magma mixing, includes three rock facies of granodiorite, enclave-rich porphyritic granite, and enclave-poor porphyritic granite. Group H intruding Croup I includes equigranular granite and micrographic granite with no evidence of magma mixing. It is suggested that the distinctively different trace element and isotopic chemistries between group I and II, support evolution from the different parental magma. It is suggested that the three rock facies in group I were generated by different degrees of magma mixing in addition to fractionation of plagioclase. MMEs experienced fractionation of biotite. The two facies in group H seem to have been generated from different parent magma from group I and evolved by fractionation of K-feldspar. The Rb-Sr whole-rock ages of the group I rocks yield $59.2\~58.9Ma$, and those of the group II rocks give 53. $3\~51.7Ma$, regardless of their distribution whether they occur in the eastern or western parts of the Yangsan Fault. Based on Sm-Nd isotope compositions, depleted mantle model ages $(T_2DM)$ of the group I range $0.8\~0.9Ga$, while those of the group II$0.6\~0.7Ga$.

• Korean Journal of Soil Science and Fertilizer
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• v.51 no.1
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• pp.16-27
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• 2018

To predict the influence of volcano eruption on agriculture in South Korea we evaluated the dispersal ranges of the volcanic ashes toward the South Korea based on the possibilities of volcano eruption in Mt. Baekdu. The possibilities of volcano eruption in Mt. Baekdu have been still being intensified by the signals including magmatic unrest of the volcano and the frequency of volcanic earthquakes swarm, the horizontal displacement and vertical uplift around the Mt. Baekdu, the temperature rises of hot springs, high ratios of $N_2/O_2$ and $_3He/_4He$ in volcanic gases. The dispersal direction and ranges and the predicted amount of volcanic ash can be significantly influenced by Volcanic Explosivity Index (VEI) and the trend of seasonal wind. The prediction of volcanic ash dispersion by the model showed that the ash cloud extended to Ulleung Island and Japan within 9 hours and 24 hours by the northwestern monsoon wind in winter while the ash cloud extended to northern side by the south-east monsoon wind during June and September. However, the ash cloud may extent to Seoul and southwest coast within 9 hours and 15 hours by northern wind in winter, leading to severe ash deposits over the whole area of South Korea, although the thickness of the ash deposits generally decreases exponentially with increasing distance from a volcano. In case of VEI 7, the ash deposits of Daejeon and Gangneung are $1.31{\times}10^4g\;m^{-2}$ and $1.80{\times}10^5g\;m^{-2}$, respectively. In addition, ash particles may compact close together after they fall to the ground, resulting in increase of the bulk density that can alter the soil physical and chemical properties detrimental to agricultural practices and crop growth.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.249-262
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• 1997

The Sr and Nd isotopic compositions of two foliated granitic plutons located in the Chonju and Sunchang area were determined in order to reconfirm the intrusion ages of granitoids and to study the sources of granitic magmas. The best defined Rb-Sr isochron for the whole rock samples of the Chonju foliated granite (CFGR) give an age of $284{\pm}12Ma$, suggesting early Permian intrusion age. In contrast, the whole rock Rb-Sr data of the Sunchang foliated granite (SFGR) scatter widely on the isochron diagram with very little variation in the $^{87}Rb/^{86}Sr$ ratios and, therefore, yield no reliable age information. Futhermore they show the concordance of mineral and whole rock Rb-Sr isochron and divide into two linear groups with roughly the same slopes and significantly different $^{87}Sr/^{86}Sr$ ratios, indicating some kind of Rb-Sr distortion in whole rock scale and a difference in source material and/or magmatic evolution between two subsets. The reconstructed isochrons of 243 Ma, which was defined from the proposed data by the omission of one sample point with significantly higher $^{87}Rb/^{86}Sr$ ratio than the others, and 252 Ma, from the combined data of it and some of this study, strongly suggest the possibility that the SFGR was intruded appreciably earlier than had previously been proposed, although the reliability of these ages still questionable owing to high scatter of data points and, therefore, further study is necessary. All mineral isochrons for the investigated granites show the Jurassic to early Cretaceous thermal episode ranging from 160 Ma to 120 Ma Their corresponding initial $^{87}Sr/^{86}Sr$ ratios correlate well with their whole rock data, indicating that the mineral Rb-Sr system of the investigated granites was redistributed by the postmagmatic thermal event during Jurassic to early Cretaceous. The initial ${\varepsilon}Sr$ values for the CFGR (64.27 to 94.81) tend to be significantly lower than those for the SFGR (125.43 to 167.09). Thus it is likely that there is a marked difference in the magma source characteristics between the CFGR and the SFGR, although the possibility of an isotopic resetting event giving rise to a high apparent initial ${\varepsilon}Sr$ in the SFGR can not be ruled out. In contrast to ${\varepsilon}Sr$, both batholiths show a highly resticted and negative values of initial ${\varepsilon}Nd$, which is -14.73 to -19.53 with an average $-16.13{\pm}1.47$ in the CFGR and -14.78 to -18.59 with an average $-17.17{\pm}1.01$ in the SFGR. The highly negative initial ${\varepsilon}Nd$ values in the investigated granitoids strongly suggest that large amounts of recycled old continental components have taken part in their evolution. Furthermore, this highly resticted variation in ${\varepsilon}Nd$ is significant because it requires that the old crustal source material, from which the granitoid-producing melts were generated, should have a reasonably uniform Nd isotopic composition and also quit similar age. Calculated T2DM model ages give an average of $1.83{\pm}0.25Ga$ for CFGR and $1.96{\pm}0.19Ga$ for SFGR, suggesting the importance of a mid-Proterozoic episode for the genesis of two foliated granites. Although it is not possible to determine precisely the source rock compositions for the investigated foliatic granites, the Sr-Nd isotopic evidences indicate that midcrustal or less probably, a lower crustal granulitic source could be the most likely candidate.

• Economic and Environmental Geology
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• v.42 no.4
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• pp.289-300
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• 2009

The Geodo mine area, had been developed for Fe and Cu ores since 1963 and abandoned in recent decades, is located in the central part of the Taebaeksan mineralized district. This area comprises of the Jangsan, Myobong, Pungchon, Hwajeol, Dongjeom, and Dumugol Formations in ascending stratigraphic order. These Formations were intruded by the Cretaceous Eopyeong granitoids that appears to produce the Geodo skarn. Their compositions are relatively oxidized quartz monzodiorite to granodiorite (magnetite series, $Fe_2O_3/FeO=0.3{\sim}1.1$). Mineralizations related skarn deposit occur in the Myobong, Pungchon, and Hwajeol Formations. The proximal skarn is zoned from andraditic garnet ($Ad_{44-95}Gr_{1-53}$) predominant adjacent to the Eopyeong granitoids to diopsidic pyroxene ($Hd_{10-100}Di_{0-89}$) predominant away from the one. The differential proportion of garnet and pyroxene is generated by water/rock ratio and their source, such as magmatic and meteoric water. This is useful tool for assessment the overall oxidation state of the entire skarn system. Gold occurs in proximal red to brownish garnet skarn, and genetically associated with Bi- and Te-bearing minerals. Skarn deposit developed in the Geodo mine area is considered as oxidized Au skarn category, based on chemical composition of the Eopyeong granitoids, zonation of skarn, and gold occurrences. Garnet-rich skarn zone will be the main target for exploration of gold in the study area. However, it is needed to the detailed survey on vertical zonation of this area as well as lateral zonation. The result of this survey would provide an important basis for the exploration of the skarn Au deposit in the Geodo mine area.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.185-199
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• 1998

Hydrogeochemical and environmental isotope studies were undertaken for various kinds of water samples collected in 1995-1996 from the Bugok geothermal area. Physicochemical data indicate the occurrence of three distinct groups of natural water: Group I ($Na-S0_4$ type water with high temperatures up to $77^{\circ}C$, occurring from the central part of the geothermal area), Group II (warm $Na-HCO_{3}-SO_{4}$ type water, occurring from peripheral sites), Group III ($Ca-HCO_3$ type water, occurring as surface waters and/or shallow cold groundwaters). The Group I waters are further divided into two SUbtypes: Subgroup Ia and Subgroup lb. The general order of increasing degrees of hydrogeochemical evolution (due to the degrees of water-rock interaction) is: Group III$\rightarrow$Group II$\rightarrow$Group I. The Group II and III waters show smaller degrees of interaction with rocks (largely calcite and Na-plagioclase), whereas the Group I waters record the stronger interaction with plagioclase, K-feldspar, mica, chlorite and pyrite. The concentration and sulfur isotope composition of dissolved sulfate appear as a key parameter to understand the origin and evolution of geothermal waters. The sulfate was derived not only from oxidation of sedimentary pyrites in surrounding rocks (especially for the Subgroup Ib waters) but also from magmatic hydrothermal pyrites occurring in restricted fracture channels which extend down to a deep geothermal reservoir (typically for the Subgroup Ia waters). It is shown that the applicability of alkaliion geothermometer calculations for these waters is hampered by several processes (especially the mixing with Mg-rich near-surface waters) that modify the chemical composition. However, the multi-component mineral/water equilibria calculation and available fluid inclusion data indicate that geothermal waters of the Bugok area reach temperatures around $125^{\circ}C$ at deep geothermal reservoir (possibly a cooling pluton). Environmental isotope data (oxygen-18, deuterium and tritium) indicate the origin of all groups of waters from diverse meteoric waters. The Subgroup Ia waters are typically lower in O-H isotope values and tritium content, indicating their derivation from distinct meteoric waters. Combined with tritium isotope data, the Subgroup Ia waters likely represent the older (at least 45 years old) meteoric waters circuated down to the deep geothermal reservoir and record the lesser degrees of mixing with near-surface waters. We propose a model for the genesis and evolution of sulfate-rich geothermal waters.