• The Journal of the Petrological Society of Korea
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• v.28 no.3
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• pp.195-215
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• 2019

Geopark is a new system for development of the local economy through conservation, education, and tourism that is an area of scientific importance for the earth sciences and that has outstanding scenic values. The Hwaseong Geopark, the candidate for Korean National Geopark is composed of 10 geosites: Gojeongri dinosaur egg fossils, Ueumdo, Eoseom, Ddakseom, Goryeom, Jebudo, Baengmiri Coast, Gungpyeonhang, Ippado and Gukwado geosites. In this study, geosites, geoheritages, and geotrails of the Hwaseong Geopark were described in detail, and the value and significane as a geopark were also discussed. The geology of the Hwaseong Geopark area belonging to the Gyeonggi Massif consists of the Precambrian metamorphic and meta-sedimentary rocks, Paleozoic sedimentary and metamorphic rocks, Mesozoic igneous and sedimentary rocks, and Quaternary deposits, indicating high geodiversity. The Gojeongri Dinosaur Egg Fossils geosite, designated as a natural monument, has a geotrail including dinosaur egg nest fossils, burrows, tafoni, fault and drag fold, cross-bedding. Furthermore, a variety of infrastructures such as eco-trail deck, visitor center are well-established in the geosite. In the Ueumdo geosite, there are various metamorphic rocks (gneiss, schist, and phyllite) and geological structures (fold, fault, joint, dike, and vein), thus it has a high educational value. The Eoseom geosite has high academic value because of the orbicular texture found in metamorphic rocks. Also, various volcanic and sedimentary rocks belonging to the Cretaceous Tando Basin can be observed in the Ddakseom and Goryeom geosites. In the Jebudo, Baengmiri Coast, and Gungpyeonghang geosites, a variety of coastal landforms (tidal flat, seastacks, sand and gravel beach, and coastal dunes), metamorphic rocks and geological structures, such as clastic dikes and quartz veins can be observed, and they also provide various programs including mudflat experience to visitors. Ippado and Gukwado geosites have typical large-scale fold structures, and unique coastal erosional features and various Paleozoic schists can be observed. The Hwaseong Geopark consists of outstanding geosites with high geodiversity and academic values, and it also has geotrails that combine geology, geomorphology, landscape and ecology with infrastructures and various education and experience programs. Therefore, the Hwaseong Geopark is expected to serve as a great National Geopark representing the western Gyeonggi Province, Korea.

• Korean Journal of Heritage: History & Science
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• v.38
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• pp.387-419
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• 2005

Material characteristics and provenance interpretation of the raw materials for the stone moulds of bronze artifacts excavated in Galdong Prehistoric site were studied. The stone moulds are made of igneous hornblendite with coarse-grained holocrystalline textures. The surface color shows greenish grey to dark green with greasy luster. The value of magnetic susceptibility of the moulds ranges from 19.2 to 71.0 (mean ; $39.2{\times}10^{-3}$ SI unit).High value of magnetic susceptibility indicates high contents of magnetite as a ferromagnetic mineral and the wide range of the values are due to heterogeneous distribution of magnetite. These are characteristics of basic igneous rocks. The rock-forming minerals of the moulds mainly consist of amphibole, plagioclase and biotite. Pyroxene, chlorite and opaque minerals are also rarely present. A large quantity of carbon was detected on the dark black crust near the surface of the moulds by quantitative analysis. Geological field survey was carried out to identify a source of the raw materials of the stone moulds around Galdong site. Hornblendite or gabbroic rocks being similar to the moulds forming rock occur at Daeseongri, Sikcheonri and Gyodongri in Jangsoo, and Illdaeri in Namwon about 50 kilometers away from the site in a straight line. They have similarity with the moulds forming rock in magnetic susceptibility ranging from 16.1 to 72.4 (mean ; $39.9{\times}10^{-3}$ SI unit). Among those hornblendite or gabbroic rocks, one in Jangsoo area is the most similar to the moulds forming rock on the basis of petrological and mineralogical characteristics. Comparing normalized patterns of major, minor, rare earth and immobile elements contents of the moulds to them of hornblendite in Jangsoo area, geochemical evolution trend and behavior characteristics show affinities between them. It suggests that the moulds forming rock and hornblendite in Jangsoo area have been originated from cogenetic magma. This hornblendite is easy to engrave an inscription or detail graphics on the surface because of its softness, and has good thermal conductivity. Hornblendite in Sikcheonri, Jangsoo is particularly produced and used for stone wares until the present day. Therefore, it is probable that the stone materials of the moulds has been imported from Daeseongri, Sikcheonri and Gyodongri in Jangsoo area. However, it cannot be completely excluded the possibility that the material of the moulds was supplied from Illdaeri in Namwon area appearing the same type of hornblendite on a small outcrops. It is necessary to carry out further archaeological studies to identify several possibilities of migration process of raw materials.

• The Journal of the Petrological Society of Korea
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• v.28 no.1
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• pp.25-38
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• 2019

The Muju-Seolcheon area, which is known to be located in the boundary of Ogcheon Belt and Ryeongnam Massif (OB-RM), consists of age unknown or Precambrian metamorphic rocks (MRs) [banded biotite gneiss, metasedimentary rocks (black phyllite, mica schist, crystalline limestone, quartzite), granitic gneiss, hornblendite], Mesozoic sedimentary and igneous rocks. In this paper are researched the structural characteristics of each deformation phase from the geometric and kinematic features and the developing sequence of multi-deformed rock structures of the MRs, and is considered the boundary location of OB-RM with the previous geochemical, radiometric, structure geological data. The geological structure of this area is at least formed through four phases (Dn-1, Dn, Dn+1, Dn+2) of deformation. The Dn-1 is the deformation which took place before the formation of Sn regional foliation and formed Sn-1 foliation folded by Fn fold. The Dn is that which formed the Sn regional foliation. The predominant Sn foliation shows a NE direction which matches the zonal distribution of MRs. A-type or sheath folds, in which the Fn fold axis is parallel to the direction of stretching lineation, are often observed in the crystalline limestone. The Dn+1 deformation, which folded the Sn foliation, took place under compression of NNW~NS direction and formed Fn+1 fold of ENE~EW trend. The Sn foliation is mainly rearranged by Fn+1 folding, and the ${\pi}$-axis of Sn foliation, which is dispersed, shows the nearly same direction as the predominant Fn+1 fold axis. The Dn+2 deformation, which folded the Sn and Sn+1 foliations, took place under compression of E-W direction, and formed open folds of N-S trend. And the four phases of deformation are recognized in all domains of the OB-RM, and the structural characteristics and differences to divide these tectonic provinces can not be observed in this area. According to the previous geochemical and radiometric data, the formation or metamorphic ages of the MRs in and around this area were Middle~Late Paleproterozoic. It suggests that the crystalline limestone was at least deposited before Middle Paleproterozoic. This deposition age is different in the geologic age of Ogcheon Supergroup which was recently reported as Neoproterozoic~Late Paleozoic. Therefore, the division of OB-RM tectonic provinces in this area, which regards the metasedimentary rocks containing crystalline limestone as age unknown Ogcheon Group, is in need of reconsideration.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.349-359
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• 2020

The Ulsan Fault Zone (UFZ) of NNW trend is developed in the Gyeongsang Basin, the southeastern part of the Korean Peninsula, and the Quaternary faults have been found around the UFZ. The faults generally thrust the Bulguksa igneous rocks of Late Cretaceous-Early Tertiary upon the Quaternary deposits or are developed within the Quaternary deposits. They mainly show the reverse-slip sense of top-to-the west movement. The lines connecting the their outcrop sites show a zigzag-form which is similar to the orientation of their fault surfaces which show the various trends, like (W)NW, N-S, (E)NE, ENE trends. The E-W trending dextral strike(-slip) fault is found in the Quaternary deposits of the Singye-ri valley. It cuts the N-S trending reverse fault and are cut by the N-S trending thrust fault again. Two types of at least two times of Quaternary tectonic movements related to the formation of neotectonic fault zone in the Singye-ri valley are considered from such the geometric and kinematic characteristics of Quaternary faults. One is the reverse faulting of N-S trend by the E-W directed 1st compression and associated the strike-slip tear faulting of E-W trend, and then the thrust faulting of N-S trend by the E-W directed 2nd compression. The other is the reverse faulting of N-S trend, and then the dextral strike-slip faulting of E-W trend by the NW-SE directed compression, and then the thrust faulting of N-S trend. In this paper is suggested the development history of Singye-ri neotectonic fault zone on the basis of the various orientations of Quaternary fault surfaces around the UFZ, and the zigzag-form connecting line of their outcrop sites, and the compressive arc-shaped lineaments which convex to the west reported recently in the Yangsan Fault Zone.

• Economic and Environmental Geology
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• v.54 no.4
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• pp.441-456
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• 2021

The Cretaceous Duwon Formation was studied on the basis of sedimentologic analysis in order to unravel geologic conditions for the development of the streamflow-dominated alluvial fan under arid to semi-arid climatic conditions. The Duwon Formation unconformably overlies the Paleoproterozoic gneiss (basement). Based on the sedimentologic analysis, the Duwon Formation is interpreted to have been deposited in gravelly braided stream (FA-1) near the basement, laterally transitional to sandy braided stream (FA-2) and floodplain environments (FA-3) with distance (< 7 km) from the basement. Lateral changes in sedimentary facies and the well development of calcrete nodules in FA-3, together with radial paleocurrent directions measured in FA-1, are suggestive of the deposition of the Duwon Formation in streamflow-dominated alluvial fan under arid to semi-arid climatic conditions. Recent analysis of detrital zircon chronology suggests that sediments of the Duwon Formation were derived from the southwestern part of the Korean peninsula, including the western part of Yeongnam Massif and the southwestern part of Okcheon Belt. This implies the alluvial fan where the Duwon Formation accumulated had the large drainage basin. Because the large drainage basin can supply the significant amounts of water and temporarily store the sediments within the basin, watery floodwater carried sediments to the alluvial fan rather than the debris flows. Furthermore, the drainage basin largely composed of coarse-grained metamorphic and igneous rocks produced sand-grade sediments, preventing evolution of floodwater into debris flows. We suggest that combined effects of the large drainage basin and its coarse-grained metamorphic and igneous rocks provided favorable conditions for the development of streamflow-dominated alluvial fan, despite arid to semi-arid climatic conditions during sedimentation.

• Economic and Environmental Geology
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• v.55 no.3
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• pp.241-259
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• 2022

In general, the REE were produced by mining conventional deposits, such as the carbonatite or the clay-hosted REE deposits. However, because of the recent demand increase for REE in modern industries, unconventional REE deposits emerged as a necessary research topic. Among the unconventional REE recovery methods, the REE-bearing coal deposits are recently receiving attentions. R-types generally have detrital originations from the bauxite deposits, and show LREE enriched REE patterns. Tuffaceous-types are formed by syngenetic volcanic activities and following input of volcanic ash into the basin. This type shows specific occurrence of the detrital volcanic ash-driven minerals and the authigenic phosphorous minerals focused at narrow horizon between coal seams and tonstein layers. REE patterns of tuffaceous-types show flat shape in general. Hydrothermal-types can be formed by epigenetic inflow of REE originated from granitic intrusions. Occurrence of the authigenic halogen-bearing phosphorous minerals and the water-bearing minerals are the specific characteristics of this type. They generally show HREE enriched REE patterns. Each type of REE-bearing coal deposits may occur by independent genesis, but most of REE-bearing coal deposits with high REE concentrations have multiple genesis. For the case of the US, the rare earth oxides (REO) with high purity has been produced from REE-bearing coals and their byproducts in pilot plants from 2018. Their goal is to supply about 7% of national REE demand. For the coal deposits in Korea, lignite layers found in Gyungju-Yeongil coal fields shows coexistence of tuff layers and coal seams. They are also based in Tertiary basins, and low affection from compaction and coalification might resulted into high-REE tuffaceous-type coal deposits. Thus, detailed geologic researches and explorations for domestic coal deposits are required.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.4
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• pp.485-505
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• 2022

On November 15, 2017, a Mw 5.4 Pohang Earthquake occurred at about 4 km hypocenter in the Heunghae area, and caused great damage to Pohang city, Korea. In the Heunghae area, which is the central part of the Pohang Basin, the Cretaceous Gyeongsang Supergroup and the Late Cretaceous to Early Paleogene Bulguksa igneous rocks as basement rocks and the Neogene Yeonil Group as the fillings of the Pohang Basin, are distributed. In this paper, structural and geological researches on the crustal deformations (folds, faults, joints) in the Pohang Basin and the coseismic ground deformations (sand volcanoes, ground cracks, pup-up structures) of Pohang Earthquake were carried out, and the deformation history of the Pohang Basin and characteristics of the coseismic ground deformations were considered. The crustal deformations were formed through at least five deformation stages before the Quaternary faulting: forming stages of the normal-slip (Gokgang fault) faults which strike (N)NE and dip at high angles, and the high-angle joints of E-W trend regionally recognized in Yeonil Group and the faults (sub)parallel to them, and the conjugate normal-slip faults (Heunghae fault and Hyeongsan fault) which strike E-W and dip at middle or low angles and the accompanying E-W folds, and the conjugate strike-slip faults dipped at high angles in which the (N)NW and E-W (NE) striking fault sets show the (reverse) sinistral and dextral strike-slips, respectively, and the conjugate reverse-slip faults in which the NNE and NNW striking fault sets dip at middle angles and the accompanying N-S folds. Sand volcanoes often exhibit linear arrangements (sub)parallel to ground cracks in the coseismic ground deformations. The N-S or (N)NE trending pop-up structures and ground cracks and E-W or (W)NW trending ground were formed by the reverse-slip movement of the earthquake source fault and the accompanying buckling folding of its hanging wall due to the maximum horizontal stress of the Pohang Earthquake source. These structural activities occurred extensively in the Heunghae area, which is at the hanging wall of the earthquake source fault, and caused enormous property damages here.

• Economic and Environmental Geology
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• v.55 no.1
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• pp.77-95
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• 2022

The Gonamsan gabbroic complex in the Pocheon area, northwestern region of South Korea consists of a variety types of gabbroic rocks and associated Fe-Ti oxide deposits caused by magmatic differentiation. Post-magmatic intrusions (i.e., gabbroic pegmatite and pyroxene-apatite-zircon rocks) partly intruded into the gabbroic rocks. The gabbroic pegmatite occurs in monzodiorite and oxide gabbro of the complex, intimately and spatially associated with high-grade lenticular Fe-Ti oxide mineralization. The pegmatite can be subdivided into plagioclase-amphibole and pyroxene-olivine pegmatite, in which the contact surface is sharp. The plagioclase-amphibole pegmatite comprises plagioclase and amphibole, with lesser amount of pyroxene, ilmenite, sphene, apatite, and biotite. The pegmatite shows plagioclase-amphibole intergranular texture, in which the open space formed by large plagioclase laths (An_2-26Ab_72-98Or_0-2) are infilled by amphibole. The pyroxene-olivine pegmatite is dark gray to black in color and also contains magnetite, ilmenite, spinel, apatite, and calcite as a minor component. The pyroxene (En_35-36Fs_8-9Wo₅₅) and olivine (Fo_84-85Fa_15-16) partly show a poikilitic texture defined by smaller euhedral olivine enclosed by coarser clinopyroxene. Fe-Ti oxide minerals consist mainly of magnetite and ilmenite that are found interstitially to earlier formed silicates. Subsequently, they are encompassed by reaction rim (almost of amphibole and biotite) along the boundary with surrounding silicate minerals. Under the microscope, magnetite contains a lot of oxyexsolved ilmenite (trellis type) and spinel, and thereby is weakly enriched in magnetite-compatible elements such as Ti, Al, Mg, and V. The structure and textures at the contact zone as well as mineralogical disequilibrium between gabbroic pegmatite and the host gabbroic rocks suggest that the pegmatite may form as a result of accumulation from Fe-rich melt (or liquid) that occurred somewhere rather than in situ form from the host gabbroic rock during the magmatic differentiation. Consequently, the preliminary study suggests that further study on the post-magmatic activities can not only help us improve our understanding on magmatic fractionation but also provide critical information on Fe-Ti oxide mineralization in gabbroic rocks resulting from the magmatic differentiation.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.169-187
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• 2023

Aggregates from 84 cities and counties in Korea were tested for quality to allow analysis of the physical characteristics of aggregates from river, land, and forest environments. River and land aggregates were analyzed for 18 test items, and forest aggregates for 12 test items. They were classified according to watershed and geology, respectively. The observed physical characteristics of the river aggregates by basin were as follows: aggregates from the Geum River basin passed through 2.5, 1.2, 0.6, 0.3, 0.15, and 0.08 mm sieves; clay lumps constituted the Nakdong River basin material; aggregates from the Seomjin River basin passed through 10, 5, and 2.5 mm sieves; those from the Youngsang River basin passed through 1.2, 0.6, 0.3, 0.15, and 0.08 mm sieves; and aggregates from the Han River basin passed through 10, 5, 2.5, 1.2, 0.6, 0.3, and 0.08 mm sieves, Stability; Standard errors were analyzed for the average amount passing through 10, 0.6, and 0.08 mm silver sieves, and performance rate showed different distribution patterns from other physical characteristics. Analysis of variance found that 16 of the 18 items, excluding the absorption rate and the performance rate, had statistically significant differences in their averages by region. Considering land aggregates by basin, those from the Nakdong River basin excluding the Geum River basin had clay lumps, those from the Seomjin River basin had 10 and 5 mm sieve passage, aggregates from the Youngsang River basin had 0.08 mm sieve passage, and those from the Han River basin had 10, 0.6, and 0.08 mm sieve passage. The standard error of the mean of the quantity showed a different distribution pattern from the other physical characteristics. Analysis of variance found a statistically significant difference in the average of all 18 items by region. Analyzing forest aggregates by geology showed distributions of porosity patterns different from those of other physical characteristics in metamorphic rocks (but not igneous rocks), and distributions of wear rate and porosity were different from those of sedimentary rocks. There were statistically significant differences in the average volume mass, water absorption rate, wear rate, and Sc/Rc items by lipid.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.233-241
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• 2024

This study was conducted to investigate the geological distribution characteristics of fluorine in rocks, which can be a major resource of forest aggregates in Korea. Samples of forest aggregates were collected from 224 sites in 22 cities and counties for this study. The national background concentration was 344 mg/kg, which was significantly lower than the average fluorine concentration of crustal, which was 625 mg/kg, and slightly higher than the average fluorine concentration of world soil, which was 321 mg/kg. In terms of region and tectonic structure, fluorine concentrations were investigated to be highest in Gyeonggi-do(394 mg/kg) and Gyeonggi massif(396 mg/kg), respectively. The concentration distribution by the origin of the parent rock was in the order of metamorphic rock(362 mg/kg) > sedimentary rock(354 mg/kg) > igneous rock(328 mg/kg), and the concentration distribution by geologic ages was the highest in the Paleozoic at 394 mg/kg. The concentration distribution by rock types was in the order of diorite(515 mg/kg) > gneisses(377 mg/kg) > schists(344 mg/kg) > phyllite(306 mg/kg) > granites(305 mg/kg) > quartz porphyry(298 mg/kg). Consequently, it is speculated that gneisses and schists, Precambrian metamorphic rocks in the Gyeonggi massif that forms the crust of Gyeonggi-do, contain high fluorine concentrations.