• Korean Journal of Mineralogy and Petrology
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• v.36 no.4
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• pp.323-336
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• 2023

We investigated the nickel potential and genesis of ultramafic rocks in the Yugu area to secure nickel resources in South Korea. The Yugu ultramafic rocks, located in the southwest of the Gyeonggi Massif, are characterized by spinel peridotite and exhibit strong serpentinization along their boundaries. The serpentinization is observed as olivine transformed to antigorite and chrysotile, while pentlandite, the nickel sulfide mineral, altered into millerite and awaruite. Serpentine displays distinct foliation, aligning subparallel to the ultramafic rock boundaries and foliation of Yugu gneiss. This suggests that the uplift of ultramafic rocks resulted in hydrothermal infiltration likely sourced from the Yugu gneiss metamorphism. The Yugu ultramafic rocks are residues after 5~18% partial melting of abyssal peridotite. Enriched light rare earth elements and Eu imply secondary metasomatism. Geochemistry suggests a link between the formation of Yugu ultramafic rock and the Triassic collision of the North and South China continents. The nickel content is around 0.17~0.21%, mainly contained in olivine and serpentine. Hence, in addition to the mineral processing study on the sulfide minerals, focused studies on oxide minerals for enhanced nickel recovery within the Yugu ultramafic rock are strongly suggested.

• Korean Journal of Environmental Biology
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• v.30 no.2
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• pp.107-120
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• 2012

This study was carried out to illiminate the diversity of vascular plants by making list of rheophyte and hydorphyte plants at Yugu stream. This study was conducted from Aug., 2009 to Sept. 2010 at 7 points. Based on the voucher specimens, vascular plants from investigated areas were 88 families 229 genera 290 species 3 subspecies 30 varieties 5 forms, totally 328 taxa. Korean endemic plants were 3 species such as Forsythia koreana (Rehder) Nakai (planted) and Paulownia coreana Uyeki (planted), and Weigela subsessilis (Nakai) L.H. Bailey. The rare and endangered plants were designated by Korea Forest Service were 4 taxa, such as Penthorum chinense Pursh, Acorus calamus L., Lilium callosum Siebold & Zucc. and Iris ensata var. spontanea (Makino) Nakai. Floristic special plants were totally 26 taxa, which were grade V of 2 taxa, grade IV of 2 taxa and grade III of 9 taxa. Naturalized plants were 27 taxa, that was 8.3% of whole discovered vascular plants in this area. Even naturalized plants has not influence on the vegetation of Yugu stream. Since village was composed along the stream and the roads and banks were linked, naturalized plants were flowed continuously into this region. So, strategy of the conservation for this region should be designed. Based on flora, 3 types of group were discriminated such as main stream type (4 points), branch stream type (2 points) and reservior type (1 point). Each group has difference in composition of plants.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.195-204
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• 2005

Interlayered structures of talc and chlorite in the talc deposits of the Yugu area are studied using transmission electron microscope. Packets of chlorite-like layer in talcs or packets of talc-like layer in chlorites are commonly observed. Randomly interlayered features of talc and chlorite are locally observed in some specimens. Reactions observed in the present study include the addition or removal of a brucite-like layer in the interlayer region of the talc or chlorite resulting in the , transformation between a talc and a chlorite layers and breakdown or formation of a talc-like layer resulting in transformation between two talc layer and one chlorite layer. Both reactions are accompanied by a significant change in volume. In addition to these mechanisms, there are two volume conserving mechanisms; the combination of both mechanisms and mutual transformation in a complex manner. Reactions from 2 chlorite layers to 3 talc layers, from 2 chlorite layers + 1 talc layers to 1 chlorite layers + 3 talc layers, and from 3 chlorite layers to 5 talc layers are observed among the complex type mechanisms.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.515-518
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• 2003

Groundwater recharge rate can be estimated from groundwater head rebound due to rainfall. Groundwater level changes are monitored for 10 months at Yugu area. Difference between two recharge rates calculated by rainfall and by effective rainfall is 1.1%~1.6%. Since this method ignores soil water percolation during groundwater level regression, the actual recharge rate may be higher than estimated one by cumulative rainfall and groundwater level change.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.253-261
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• 2024

Olivine, a major mineral in the upper mantle with strong intrinsic elastic anisotropy, plays a crucial role in seismic anisotropy in the mantle, primarily through its lattice preferred orientation (LPO). Despite this, the influence of the microstructure of mylonitic rocks on seismic anisotropy remains inadequately understood. Notably, there is a current research gap concerning seismic anisotropy directly inferred from mylonitic peridotite massifs in Korea. In this study, we introduce the deformation microstructure and LPO of olivine in the mantle shear zone. We calculate the characteristics of seismic anisotropy based on the degree of deformation (proto-mylonite, mylonite, ultra-mylonite) and establish correlations between these characteristics. Our findings reveal that the seismic anisotropy resulting from the olivine LPO in the ultra-mylonitic rock appears to be the weakest, whereas the seismic anisotropy resulting from the olivine LPO in the proto-mylonitic rock appears to be the strongest. The results demonstrate a gradual decrease in seismic anisotropy as the fabric strength (J-index) of olivine LPO diminishes, irrespective of the specific pattern of olivine's LPO. Moreover, all samples exhibit a polarization direction of the fast S-wave aligned subparallel to the lineation. This suggests that seismic anisotropy originating from olivine in mylonitic peridotites is primarily influenced by fabric strength rather than LPO type. Considering these distinctive characteristics of seismic anisotropy is expected to facilitate comparisons and interpretations of the internal mantle structure and seismic data in the Yugu area, Gyeonggi Massif.

• Journal of the Mineralogical Society of Korea
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• v.10 no.1
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• pp.33-44
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• 1997

The reaction path of water-gneiss in 200m borehole at the Soorichi site of Yugu Myeon, Chungnam was simulated by the EQ3NR/EQ6 program. Mineral composition of borehole core and fracture-filling minerals, and chemical composition of groundwater was published by authors. In this study, chemical evolution of groundwater and formation of secondary minerals in water-gneiss system was modelled on the basis of published results. The surface water was used as a starting solution for reaction. Input parameters for modelling such as mineral assemblage and their volume percent, chemical composition of mineral phases, water/rock ratio reactive surface area, dissolution rates of mineral phases were determined by experimental measurement and model fit. EQ6 modelling of the reaction path in water-gneiss system has been carried out by a flow-centered flow through open system which can be considered as a suitable option for fracture flow of groundwater. The modelling results show that reaction time of 133 years is required to reach equilibrium state in water-gneiss system, and evolution of present groundwater will continue to pH 9.45 and higher na ion concentration. The secondary minerals formed from equeous phase are kaolinite, smectite, saponite, muscovite, mesolite, celadonite, microcline and calcite with uincreasing time. Modeling results are comparatively well fitted to pH and chemical composition of borehole groudwater, secondary minerals identified and tritium age of groundwater. The EQ6 modelling results are dependent on reliability of input parameters: water-rock ratio, effective reaction surface area and dissolution rates of mineral phases, which are difficult parameters to be measured.

• Journal of Wetlands Research
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• v.18 no.4
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• pp.350-356
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• 2016

The biggest factor in the success of breeding animals is selection of foods, which is determined by quality and quantity of habitats(Newton, 2003), in the case of This high biomass wetlands as an indicator of ecosystem function about Common Kestrel's choice of hunting area is expected to be an important clue of quality and quantity of habitats. For this study, it is divided into four types(Glasslands, Paddy fields, Dry fields, Rparian land) about Common Kestrel's hunting area in Yugu-eup, Gongju-si, Chungcheongnam-do, Recorded the behavior of Common Kestrel for three years during the breeding season from March to June(2014~2016). Result of investigation, hunting area showed a high hunting behavior in riversides and flight-hunting was frequently investigated from may to June. In addition flight-hunting's main food acquisition is mammal(the vole), while perching behavior's main food acquisition is insect according to the fact flight-hunting were mainly done in riversides, perching behavior were highly investigated than flight-hunting at glasslands and paddy fields and dry field. Hunting spot's coverage rate of plants covering the ground showed differences depending on hunting areas, but height of plants were not significant. Height of the plant according to hunting methods of flight-hunting to catch mammal(vole) was analyzed to prefer lower height than perching behavior Based on these results riversides are considered as a very important environmental factors for Common Kestrel's prey selection in breeding session.

• Economic and Environmental Geology
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• v.49 no.4
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• pp.249-267
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• 2016

The Hongseong area of the central-western Korean Peninsula is considered to be a part of collision zone that is tectonically correlated to the Qinling-Dabie-Sulu belt of China. The area includes the elliptical-shaped serpentinized ultramafic bodies, together with mafic rocks. The studied bodies are in contact with the surrounded Neoproterozoic alkali granites at the Baekdong and Wonnojeon bodies and the Paleoproterozoic Yugu gneiss at the Bibong body. The Baekdong body contains the blocks of the Neoproterozoic alkali granites and the Late Paleozoic metabasites. The Bibong body also includes the Neoproterozoic alkali granite blocks. The Mesozoic intrusive rocks are also recognized at the Baekdong, Wonnojeon and Bibong bodies. On the other hand, the Early Cretaceous volcanic rocks are occurred at the Bibong body. The detrital zircon SHRIMP U-Pb ages of the serpentinites at three bodies range variously from Neoarchean to Middle Paleozoic at the Baekdong body, and from Neoarchean to Early Cretaceous at the Wonnojeon and Bibong bodies. Although serpentinization does not generally produce minerals suitable for direct isotopic dating, the youngest Middle Paleozoic age at the Baekdong body and the Early Cretaceous age at the Wonnojeon and Bibong bodies indicate the possible upper age limit for the (re)serpentinization. Especially, the Early Cretaceous serpentinization ages may be related to the widespread Early Cretaceous igneous activity in the central-southern Korean Peninsula. Age results for the serpentinite bodies and the included blocks of the studied serpentinized ultramafic bodies in the Hongseong area, therefore, provide several possible interpretations for the serpentinization ages of the ultramafic rocks as well as the geotectonic implications of serpentinization, requiring more detailed study including other serpentinized ultramafic bodies in the Hongseong area.

• Journal of Environmental Impact Assessment
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• v.23 no.4
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• pp.271-284
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• 2014

The objectives of this research were to analyse the microhabitat of Cobitis choii which is designated as an endangered fish species (I) and national monument species in Korea (No. 454), and provide valuable information of suitable replacement habitat in the future for a conservation of the population with rapid decreases by environmental pollution. Sampling and microhabitat analysis in three streams such as Baekgok, Yugu and Gap Stream, known as one of the least habitats in Korea showed that the mean number of Cobitis choii observed was 2.6. This result indicated that the richness was too low, so the species conservation was very urgent. Optimal physical microhabitat of the population was determined as environmental conditions with > 60% sand with 1 mm particle size, optimal water depth of 20 - 60 cm in the habitats, and the optimal current velocity of < 0.4 m/s. Under the circumstances of the microhabitat, optimal water volume (discharge) was 0 - 2 m3/s in the each sectional analysis and this reach was mainly composed of the stream section with intermittant slow runs and pools. These microhabitats were largely disturbed by physical modifications of habitat and chemical pollutions due to direct influences of nutrient-rich water inputs from the urban area and intensive agricultural pollutants. For these reasons, optimal habitat replacement are required in the future for the conservation of the species.

• Economic and Environmental Geology
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• v.43 no.4
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• pp.333-341
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• 2010

Fluvial sediments are widely distributed in present and old river-beds of the mid-Keum River, the tributaries of which are the Yugu and Jeongan Rivers. The basement of the mid-Keum River area consists of Mesozoic granites which are easily eroded compared to Precambrian gneisses, which are exposed in the upper-Keum River area. The provenance of the fluvial sediments includes both the Precambrian gneisses and Mesozoic granites, which occur in the catchment of the mid-Keum River. The coarse-grained sediments were probably transported from the river-beds and the overbank floodings of the main Keum River and its tributaries when the climate was warm and wet. The oldest mud deposits were dated at ca. 9,400 yr BP by the radiocarbon method. It has been estimated that the sand deposits below the dated muds were formed in a period from the Late Pleistocene to the Early Holocene. However we have revealed that the major part of the present river-bed sediments was formed at ca. 3,000-6,000 yr BP, i.e., in the mid- to late Holocene, when summer monsoon was very strong due to climatic changes. We have calculated fluvial sedimentation rates of 0.12-0.16 cm/yr and 0.02-0.09 cm/yr for borehole KJ-29 river-bed sediments and borehole KJ-28 floodplain deposits, respectively. We conclude that the sedimentation rate is higher near the present stream channel than near the floodplain.