• Economic and Environmental Geology
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• v.52 no.5
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• pp.395-407
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• 2019

The duplex system has been considered as an important slip-transfer mechanism to evaluate the evolution of orogenic belts. Duplexes are generally found in the hinterland portion of fold-thrust belts and accommodate large amounts of total shortening. Thus, understanding its geometric and kinematic evolution can give information to evaluate the evolution of the entire orogenic belt. Duplexes are recognized as closed-loop thrust traces on map view, indicating higher connectivity than imbricate fans. As originally defined, a duplex is an array of thrust horses which are surrounded by thrust faults including the floor and roof thrusts, and imbricate faults between them. Duplexes can accommodate regional layer-parallel shortening and transfer slip from a floor thrust to a roof thrust. However, an imbricate fault is not the only mean for layer-parallel shortening (LPS) and displacement transfer within duplexes. LPS cleavages and detachment folds can also play the same role. From this aspect, a duplex can be divided into three types; 1) fault duplex, 2) cleavage duplex and 3) fold duplex. Fault duplex can further be subdivided into the Boyer-type duplex, which was firstly designed duplex system in the 1980s that widely applied most of the major fold-thrust belts in the world, and connecting splay duplex, which has different time order in the emplacement of horses from those of the Boyer-type. On the contrary, the cleavage and fold duplexes are newly defined types based on some selected examples. In the Korean Peninsula, the Yeongwol area, the western part of the Taebaeksan Zone of the Okcheon Belt, gives an excellent natural laboratory to study the structural geometry and kinematics of the closed-loops by thrust fault traces in terms of a duplex system. In the previous study, the Yeongwol thrust system was interpreted by alternative duplex models; a Boyer-type hinterland-dipping duplex vs. a combination of major imbricate thrusts and their connecting splays. Although the high angled beds and thrusts as well as different stratigraphic packages within the horses of the Yeongwol duplex system may prefer the later complicate model, currently, we cannot choose one simple answer between the models because of the lack of direct field evidence and time information. Therefore, further researches on the structural field investigations and geochronological analyses in the Yeongwol and adjacent areas should be carried out to test the possibility of applying the fold and cleavage duplex models to the Yeongwol thrust system, and it will eventually provide clues to solve the enigma of formation and its evolution of the Okcheon Belt.

• Journal of Conservation Science
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• v.12 no.1 s.15
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• pp.31-47
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• 2003

The stone implements from the Unjeonri relic sites were studied on the basis of petrology, geochemistry and archaeogeological interpretations. Magnetic susceptibility (MS) of the stone implements were mainly lest than 0.5 $(10^{-3}\;SI\;unit)$, however, stone axe of syenitic rock (2.37), stone axe of schist (0.19) and stone knife of slate (0.11) showed different from the some measured rocks of an outcrop. Geochemical evolution trend of both a stone implement and the surface rock were identical when it a normalization to use the behavior, enrichment, compatibility and incompatibility of the elements. But, some rocks of a axe (schist), a knife (slate), a arrowhead (shale) could not confirm typical occurrence and the distribution area within the Unjeonri site and a radius 10 km. In the Unjeonri site, the stone implements suggest that coexisting two types as domestic- and foreign-type lithic artifacts.

• Journal of the Mineralogical Society of Korea
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• v.26 no.4
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• pp.285-297
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• 2013

Ilmenite deposits are developed along the Precambrian intercumulated anorthosite body in Jikjeon-Ri, Bukcheon-Myeon, Hadong, Korea. Both detailed geological survey and drilling prospecting data for seven boreholes can be used to do resource estimation with GOCAD S/W. 3D modeling using geostatistics is applied to predict the shape and size of Ti ore bodies. As a result, 5 Ti ore veins occurred along N-S direction and average grade of Ti and ilmenite resources are calculated as 2.98 wt% Ti and 7,494,303 metric tons ilmenite ore reserves (Ti 223,330 t). This 3D modeling will be applied to the whole ilmenite deposits in Hadong-Sancheong area to predict the exact distribution and resources estimations of Ti ores.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.110-115
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• 1998

Self-potential, VLF-EM and dipole-dipole resistivity methods have been widely used for exploration of conductive sulfide ore deposit, because of the convenience and low cost of field work and the reliability of their results. The geophysical responses for vein-type sulfide outcrop of Changkoom mine located in Bukwi-Myon, Jinan-Gun, Chollabuk-Do were investigated and compared with its drilling results. The geology around the survey area is composed of acidic volcanics and sediments of Yuchon Group. And sulfides bearing pyrite, pyrrotite, galena etc. are deposited in disseminated or vein type within acidic volcanics. Typical geophysical responses were detected from the above vein type ore body, respectively. From the shape and extent of S.P. anomaly, ore body is dipping westward and extending about 50 m. It is detected that the VLF EM response matching the outline of ore zone is considered as indication of dyke dipping westward. And also resistivity response indicating conductive dipping dyke is detected. From drilling results for outcrop and geophysical anomalies, the shape of ore body is vein type dipping about $70^{\circ}W$ and extending about 50 m.

• Journal of the Korean earth science society
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• v.39 no.6
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• pp.545-554
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• 2018

The Cretaceous Eumsung (Eumseong) Basin is a pull-apart basin, formed along a series of the Gongju strike-slip faults trending NE-SW. The Nongdari-Meer forest of the Gugokri area in the southwestern part of the basin is comprised of thick purple mudstone, intercalating conglomerate, pebbly sandstone, and green mudstone beds. The succession mainly consists of seven sedimentary facies: stratified conglomerate (C2), conglomerate encased in siltstone (CE), stratified pebbly sandstone encased in siltstone (PSE2), purple sandy siltstone (Zp), green sandy siltstone (Zg), purple mudstone (Mp), and green mudstone (Mg). Sedimentary environment is mainly indicative of alluvial-plain setting in an alluvial-to-lacustrine sedimentary system, developed in the southwestern part of the basin. Geological survey was fulfilled in succession of the Gugokri sedimentary system using 1:5000 topographic map, which resulted in a geological route map. This study newly suggested that there be fluvial systems showing ENE and NNE trends in the study area, based on data of palaeocurrent direction and sedimentary characteristics in new outcrops of the forest. The study also revised the precedent sedimentation model of the Gugokri system.

• Economic and Environmental Geology
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• v.34 no.6
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• pp.627-648
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• 2001

At least two distinct types of layering are present in the middle zone of the Skaergaard intrusion; alternating plagioclase-rich and pyroxene-rich, macro-rhythmic layers, and smaller scale, modally-graded, rhythmic layers. The macro-rhythmic layers are ubiquitous in the middle zone of the Layered Series, but are not observed in the lower and upper zone of the Layered Series or in the wall or roof tories of the intrusion. They range from 0.3 to 17.3 m in thickness, have sharp upper and lower boundaries, and can be traced laterally for over 2 ]fm in outcrop. Although individual macrorhythmic layers are not internally graded, many contain smaller-scale, modally-graded layers. Modally-graded. rhythmic layers are a common feature of the Layered Series but are not abundant in either the Upper Border Series or the Marginal Border Series. They range in thickness from 1 to 50 cm and can be traced laterally in outcrop for up to 100 m. Their lateral termination ranges from abrupt to gradational, and they are often associated with cut and fill structures and crossbedding suggestive of current activity. They are characterized by sharp lower and gradational upper contacts, and by strong intra-layer modal grading with olivine, ilmenite, and magnetite concentrated at the base, pyroxene concentrated above the base, and plagioclase concentrated at the top. The layers are also grain-size graded with the maximum size for each phase occurring at the horizon in the layer where the phase is most abundant. Modally-graded, rhythmic layers in the middle zone of the Layered Series occur within both plagioclase-rich and pyroxene-rich macro-rhythmic layers.

• Economic and Environmental Geology
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• v.52 no.1
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• pp.107-118
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• 2019

Two assertions about the process the formation of the high-purity limestone in the Taebaeksan Basin, categorized into syngenetic and epigenetic origin, are verified on the basis of its oxygen-carbon stable isotopic characteristics. The carbonate rocks sampled from the selective six high-purity limestone mines and several outcrops in the Daegi formation are featured by various colors such as the gray, light gray and dark gray. They show a wide range of oxygen stable isotope ratios (4.5 ~ 21.6 ‰), but a narrow range of carbon stable isotope ratios (-1.1 ~ 0.8 ‰, except for vein calcite), which means that they had not experienced strong hydrothermal alteration. In addition, there is no difference in the range of the oxygen stable isotope ratios by mine and color, and it is similar to the range from surrounding outcrop samples. These results indicate that the effect of the hydrothermal alteration were negligible in the generation of high-purity limestone in deposit scale. Whereas, the carbonate rocks can be divided texturally into two groups on the basis of an oxygen isotope ratio; the massive-textured or well-layered samples (>15 ‰), and the layer-disturbed (or layer-destructed) and showing over two colors in one sample (<15 ‰). In the multi-colored samples, the bright parts are characterized by the very low oxygen stable isotope ratios, compared to the dark parts, implying the increase in brightness of the carbonate rocks could be induced by the interaction between hydrothermal fluid and rock. However, these can be applied in a small scale such as one sample and are not suitable for interpretation of the generation of high-purity limestone as a deposit scale. In particular, the high oxygen isotope ratios from the recrystallized white limestone suggest that hydrothermal fluids are also rarely involved during recrystallization process. In addition, the occurrences of the high-purity limestone orebody strongly support the high-purity limestone in the area are syngenetic rather than epigenetic; the high-purity limestone layers in the area show continuous and almost horizontal shapes, and is intercalated between dolomite layers. Consequently, the overall reinterpretation based on the sequential stratigraphy over the Taebaeksan basin would play an important role to find additional reserves of the high-purity limestone.

• The Journal of the Petrological Society of Korea
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• v.27 no.2
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• pp.85-96
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• 2018

The Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks are distributed in the Eoraesan area, Chungju which is located in the northwestern part of Ogcheon metamorphic zone, Korea, and the rare earth element (REE) mineralized zone has been reported in the Gyemyeongsan Formation. We drew up the detailed geological map by the lithofacies classification, and measured the radioactivity values of the constituent rocks to understand the distribution and characteristics of the source rocks of REE ore body in this paper. It indicates that the Neoproterozoic Gyemyeongsan Formation is mainly composed of metapelitic rock, granitic gneiss, iron-bearing quartzite, metaplutonic acidic rock (banded type, fine-grained type, basic-bearing type, coarse-grained type), metavolcanic acidic rock, and the Mesozoic igneous rocks, which intruded it, are divided into pegmatite, biotite granite, gabbro, diorite, basic dyke. The constituent rocks of Gyemyeongsan Formation show a zonal distribution of mainly ENE trend, and the distribution of basic-bearing type of metaplutonic acidic rock (MPAR-B) is very similar to that of the previous researcher's REE ore body. The Mesozoic biotite granite is regionally distributed unlike the result of previous research. The radioactive value of MPAR-B, which has a range of 852~1217 cps (average 1039 cps), shows a maximum value among the constituent rocks. The maximum-density distribution of radioactive value also agrees with the distribution of MPAR-B. It suggests that the MPAR-B could be a source rock of the REE ore body.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.483-494
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• 2007

The properties of fracture system on road-cut slopes along the Busan-Ulsan express way under construction are investigated and analyzed. Fracture spacing distributions show log-normal form with extension fractures and negative exponential form with shear fractures. Straight line segments in log-log plots of cumulative fracture length indicate a power-law scaling with exponents of -1.13 in site 1, -1.01 in site 2 and -1.52 in site 3. It is likely that the stability and strength of rock mass are the lowest in site 1 as judged from the analyses of spacing, density and inter-section of fractures in three sites. In contrast, the highest efficiency of the fracture network for conducting fluid flow is seen in site 3 where the largest cluster occupies 73% through the window map. Based on the field survey data, this study modified weighting values of the RMR system using a multiple regression analysis method. The analysis result suggests a modified weighting values of the RMR parameters as follows; 18 for the intact strength of rock; 61 for RQD; 2 for spacing of discontinuities; 2 for the condition of discontinuities; and 17 for ground water.

• Economic and Environmental Geology
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• v.57 no.1
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• pp.93-105
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• 2024

Chilgok Geummubong tree fern fossil site is the type locality where tree fern stem fossils (Cyathocaulis naktongensis) were first discovered by Tateiwa in 1925. Recognized for its academic value, it was designated as a natural monument in the 1930s during the Japanese colonial period, and preserved and managed for over 90 years. However, at the time of discovery, the stratigraphic level of tree fern fossils could not be located because the fossils were fragments detached from the rock body, and thus the Geummubong area where the conglomerate/sandstone layers of the Nakdong Formation are distributed, has been designated as a cultural heritage area. Only in the 2000s, when tree fern fossils were directly recovered from the outcrops near the designated area, the sedimentary rock facies containing the fossils were interpreted, and the anatomical characteristics of the Mesozoic tree fern fossils could be described and identified as a species level. Such studies are, in these days, redefining classification criteria done by Japanese paleontologist, Ogura. That is, Korean researchers pointed out that the classification criteria of the tree fern fossils (Cyathocaulis) reported early from Chilgok were ambiguous, and the possibility that the two species were the same species was suggested. In addition, it is necessary to reorganize designated areas as a way to resolve social conflicts and civil complaints caused by various regulations that have continued for a long time.