• Economic and Environmental Geology
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• v.41 no.3
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• pp.275-286
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• 2008

The Sambo gold deposit located nearby the Cretaceous Hampyeong basin is composed of gold quartz fine vein(the Jija vein) within Cretaceous rhyolite showing $N10{\sim}20W$ trends as well as $N5{\sim}10E$ trending quartz veins(the Pungja, Gwangsan and Pungjaji veins) in Precambrian gneiss. The gold vein typically displays the intermittent and irregular fine veins within rhyolite. Electrum is disseminated in wallrock along the fine cracks as well as coexists with hematite replacing pyrite. Ore-forming fluids from the mineralized vein($H_2O/-NaCl$ system, Th; $340{\sim}200^{\circ}C$, Salinity <2.7 eq. wt.% NaCl) and NE-trending veins($H_2O-NaCl/-CO_2$ system, Th; $400{\sim}190^{\circ}C$, salinity <7.9 eq. wt.% NaCl) are featured by dissimilar physicochemical conditions but their fluid evolution trends(boiling and mixing) are similar with each other. Gold veins of the Sambo deposit filled along NNW-trending tension crack are related to pull-apart basin evolution. Selective gold mineralization of the deposit reflect to dissimilarity between two ore-forming fluid sources. Consequently, gold veining of the Sambo deposit formed at shallow-crustal level and could be categorized into epithermal-type gold deposit related to tensional fractures filling triggered by Cretaceous geodynamics.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.508-517
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• 2011

The linear cutting test is the most reliable and accurate approach to measuring cutting forces and cutting efficiency using full-size disc cutter in various rock types. The result of linear cutting tests can be used to obtain the key parameters of cutter-head design (i.e. optimum cutter spacing, cutter forces). In Korea, LCM (Linear Cutting Machine) tests have been performed for typical Korean rock types, but these studies focused on the isotropic rocktypes. For prediction of TBM (Tunnel Boring Machine) performances in complex geological conditions including a bedded and schistose rockmass, it is important to consider the effects of anisotropy of rockmass on cutting performances and cutting efficiency. This study discusses a series of LCM tests that were performed for Asan Gneiss having two types of anisotropy angles to assess the effect of the anisotropy angle on rock-cutting performances of TBM. The result shows that the rock-cutting performances and optimum cutting conditions are affected by anisotropy angle and the effect of anisotropy on rock strength should be considered in a prediction of the cutting performances and efficiency of TBM.

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.52-74
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• 2000

The basement rock of upper stream of Keum River Valley consists of Precambrian gneiss which is resistant to weathering. That of mid and lower stream valley, however, is mainly composed of Mesozoic granites which are vulnerable to weathering. The upstream part of Geum River Basin is typified by the deeply-incised and steep meandering streams, whereas mid and lower part is characterized by wide floodplain and gently dipping river bottom toward the Yellow Sea. In particular flooding deposits, in which are imprinted a number of repetitions of erosion and sedimentation during the Holocene, are widely distributed in the lower stream of Geum River Basin. For understanding of erosions in the mid and lower stream of Geum River Basin, the rate of erosion of each small basins were estimated by using the data of field survey, erosional experiments and GIS ananlysis. It was revealed that erosion rate appeared highest in granite areas, and overall areas, in this field survey were represented by relatively high erosion rates. By implemeatation of remote sensing and imagery data, the temporal changes of river bed sediments for about last 11 years were successfully monitored. Observed as an important phenomenon is that the river bed has been risen since 1994 when an embankment (Dyke) was constructed in the estuarine river mouth. From the results derived from the detailed river bed topographical map made in this investigation, the sedimentation of the lower river basin is considered to be deposited with about 5 cm/year for the last 11 years. Based on this river bed profile analysis by HEC-6 module, it is predicted that Geum River bed of Ganggyeong area is continuously rising up in general until 2004. Although extraction of a large amount of aggregates from Gongju to Ganggyung areas, the Ganggyung lower stream shows the distinct sedimentation. Therefore, it is interpreted that the active erosions of tributary basins Geum drainage basins can affect general river bed rising changes of Geum River.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.35-45
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• 2010

The soil tests have been performed on the specimens obtained from about 1,150 sites including landslides and non-landslides areas in natural terrains for last 10 years. Based on the results of those tests, the average soil properties are estimated and the simple equations for estimating permeability are proposed according to geologic conditions. The average permeability in Granite and Mudstone sites is higher than other sites and the content of silt and clay in Mudstone and Gneiss sites is higher than other sites. The correlation analysis and the regression analysis were performed to estimate the coefficient of permeability according to geological conditions. As the result of the correlation analysis, the coefficient of permeability is selected as a dependent variable, and the silt and clay contents, the water contents and the dry unit weights are selected as independent variables. As the result of the regression analysis, the silt and clay contents and the void ratio were involved commonly in the linear regression equations according to geological conditions. To verify the proposed the linear regression equations, the measured result of the coefficient of permeability at other sites was compared with the result predicted with the proposed equations. As the result of comparison, there were a little bit different between them for some data. However the difference was relatively small. Therefore, the linear regression equations for estimating the coefficient of permeability according to geological conditions may be applied to Korean soils. However, these equations should be verified and corrected continuously to improve the accuracy.

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.1-19
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• 1995

In order to characterize the petrogenesis of the E-W trending Imjinganag belt, we studied the metamorphic rocks of the Yeoncheon Group near its type locality, Yeoncheon - Cheongok area, belonging to the southern part of this fold-thrust belt. The Samgot Formation of the Yeoncheon Group consists of calc-silicate and metapsammitic rocks together with amphibolite and amphibole gneiss. Layers of these metamorphic rocks concordantly occur in a wide area with its length greater than 15 km along their strike direction. Major mineral assemblages of the amphibolite are hornblende + plagioclase ${\pm}$ garnet ${\pm}$ diopside ${\pm}$ biotite ${\pm}$ quartz. Accessory rutile and ilmenite are characteristically replaced by titanite. Metamorphic temperatures and pressures estimated from the garnet - hornblende - plagioclase - quartz geothermo-barometers are 632-$736^{\circ}C$ and 7.9-11.1 kbar, respectively. Thus, the regional metamorphism of the study area belongs to the upper amphibolite facies. Furthermore, Sm-Nd and Rb-Sr data of garnet, plagioclase, and whole rock of an amphibolite define mineral isochrons of $231{\pm}30$ Ma and $222{\pm}24$ Ma, respectively, suggesting the Triassic metamorphism. These results are consistent with P-T conditions and metamorphic ages reported in the Shandong Peninsula, and support the hypothesis that the Chinese collision belt may extend into the Imjingang belt in the Korean Peninsula.

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.20-30
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• 1995

We report major element chemistry of the Chuncheon amphibolite in the Precambrian Kyonggi massif and discuss its origin. On the basis of areal distribution and chemical difference, the Chuncheon amphibolite can be divided into the Gubongsan arnphibolite in the Gubongsan Group east of Chuncheon city and the Sangguli amphibolite in the Yongduri gneiss complex occurring to the southeast of the Gubongsan Group. Overall major element characteristics of the Chuncheon amphibolite indicate an igneous precursor, although it shows concordant relationship with metasedimentary rocks in many cases. The parental rock of the amphibolite has tholeiitic composition with 45-53wt% $SiO_2$. The Sangguli amphibolite has lower MgO than the Gubongsan one. The difference in $TiO_2$/P_2O_5 ratio between the two amphibolites suggests that they are not genetically related. In MgO variation diagrams, $Na_2O$, $Fe_2O_3$ and $Al_2O_3$ show scattered pattern, while MgO has positive correlation with CaO and negative one with $SiO_2$, $TiO_2$, $P-2O_5$ and $K_2O$. These variations can be interpreted as the result of differentiation of basaltic magma with fractionation of olivine, pyroxene, and plagioclase. Tectonic discrimination using major elements generally suggest withinplate environment for the Chuncheon amphibolite which is similar to that of the amphibolite in the Ogcheon belt.

• International Journal of Highway Engineering
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• v.8 no.4 s.30
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• pp.135-143
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• 2006

This study evaluated the fatigue resistance characteristics of hot-mix recycled asphalt mixtures which were prepared by a new blending method. Since the binder of RAP shows higher viscosity without being rejuvenated in the ordinary recycled mixture, this new(modified) blending method was developed for obtaining more uniform level of binder viscosity in the recycled mixture. Cold-planned RAP was collected and mix design was performed using 15% RAP content for two virgin aggregate, gneiss and granite. Penetration grade of 60-80 asphalt was used in mixing recycled mixture together with a polymer modifier, LDPE. Indirect tensile fatigue tests were carried out to evaluate characteristics of fatigue resistance of performance of recycled asphalt mixtures. The recycled mixtures with LDPE 6% showed higher repeated loading fatigue life. Fatigue life ratio of new(N) mixing method mixtures was approximately 0.6-0.7 before aging and 0.8-1.0 after aging treatment of ordinary(O) mixing method mixture. This means the N mixture becomes stronger with aging process increase. If further aging is treated, N mixture may be showing stronger resistance than O mixture.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.304-317
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• 2009

Most crystalline rocks have much higher compressive strength than tensile strength and show brittle failure. In-situ rock mass, strong enough in general sense, often fails in brittle manner when subjected to high stress exceeding strength in due of geometrically induced stress concentration or of high initial stress. Therefore, it is necessary to verify the brittle failure characteristics of rock and rock mass for proper stability assessment of underground structures excavated in great depths. In this study, damage controlled tests were conducted on biotite-granite and granitic gneiss, which are the two major crystalline rock types in Korea, to obtain the strain dependency characteristics of the cohesion and friction angle. A Cohesion-Weakening Friction-Strengthening (CWFS hereafter) model for each rock type was constructed and a series of compression tests were carried out numerically while varying confining pressures. The same tests were also conducted assuming the rock is Mohr-Coulomb material and results were compared.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.197-207
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• 1997

Rocks in the Cheongsong mine area consist of Precambrian gneiss, Cretaceous sedimentry rocks and late Cretaceous quartz porphyry. The Cheongsong deposit is composed of many hydrothermal quartz veins of strikes $N30^{\circ}{\sim}60^{\circ}W$, dips $60{\sim}85^{\circ}E$ which fill WNW fault system. Pyrite and hematite occur within transparent quartz near margins of early stage II, and milky quartz of middle stage II coexists with sphalerite, chalcopyrite and galena coexisting with Cu-Pb-Bi minerals in center part of stage II quartz veins. Stage III calcite vein filled cracks or fractures of earlier quartz veins contains native copper and chalcopyrite. Supergene minerals are chalcocite, covellite, malanchite and chrysocolla. Alteration minerals are sericite, chlorite, argillite, epitode and pyrite. Ranges of salinities and homogenization temperatures for fluid inclusions in the individual periods of stage II are: 3.7 to 7.8 wt.% eq. NaCl and 200 to $380^{\circ}C$ in transparent quartz of early stage II; 0.7 to 6.4 wt.% eq. NaCl and 200 to $320^{\circ}C$ in milky quartz of middle stage II; 0.0 to 0.9 wt.% eq. NaCl and 250 to $320^{\circ}C$ in calcite of late stage II. Those of stage III calcite range about 0 wt.% eq. NaCl, and from 140 to $260^{\circ}C$, respectively. The relationship between salinities and temperatures shows decrease tendency with paragenetic time from stage II to III. The ${\delta}^{18}O_{H_2O}$ value is 0.5‰ in stage I, range from 0.5 to -0.4‰ in stage II, and from -3.2 to -3.7‰ in stage III. Calcite in the stage II and stage III has ${\delta}^{13}C$ values of -5.0‰ and -4.5 to -4.9‰, respectively. There is a decrease in sulfur fugacity values with paragenetic time of stage II, from $10^{-6.3}$ atm for early mineralization, to $10^{-6.5}$ atm for middle stage, to $10^{-8.0}$ atm for late mineralization of stage II. The results of stable isotope and fluid inclusion indicate that ore fluids reacted with meteoric water and wall rock in the Cheongsong hydrothermal system.

• Economic and Environmental Geology
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• v.21 no.2
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• pp.149-164
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• 1988

Electrum-sulfide mineralization of the Samgwang and Sobo mines of the Cheongyang Au-Ag area was deposited in two stages of quartz and calcite veins that fill fault zones in granite gneiss. Radiometric dating indicates that mineralization is Early Cretaceous age (127 Ma). Fluid inclusion and sulfur isotope data show that ore mineralization was deposited at temperatures between $340^{\circ}$ and $180^{\circ}C$ from fluids with salinities of 1 to 8 wt. % equiv. NaCl and a ${\delta}^{34}S_{{\sum}S}$ value of 2 to 5 per mil. Evidence of fluid boiling (and $CO_2$ effervescence) indicates a range of pressures from < 200 to $\approx$ 700 bars, corresponding to depths of ${\approx}1.5{\pm}0.3\;km$ in a hydrothermal system which alternated from lithostatic toward hydrostatic conditions. Au-Ag deposition was likely a result of boiling coupled with cooling. Meaured and calculated hydrogen and oxygen isotope values of ore-forming fluids indicate a significant meteoric water component, approaching unexchanged paleometeoric water values. Comparison of these values with those of other Korean Au-Ag deposits reveals a relationship among depth, Au/Ag ratio and degree of water-rock interaction. All investigated Korean Jurassic and Cretaceous gold-silver-bearing deposits have fluids which are dominantly evolved meteoric waters, but only deeper systems (${\geq}1.5\;km$) are exclusively gold-rich.