• 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.

• Economic and Environmental Geology
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• v.25 no.3
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• pp.337-349
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• 1992

The Tertiary basins in Korea have widely been studied by numerous researchers producing individual results in sedimentology, paleontology, stratigraphy, volcanic petrology and structural geology, but interdisciplinary studies, inter-basin analysis and basin-forming process have not been carried out yet. Major work of this study is to elucidate evidences obtained from different parts of a basin as well as different Tertiary basins (Pohang, Changgi, Eoil, Haseo and Ulsan basins) in order to build up the correlation between the basins, and an overall picture of the basin architecture and evolution in Korea. According to the paleontologic evidences the geologic age of the Pohang marine basin is dated to be late Lower Miocence to Middle Miocene, whereas other non-marine basins are older as being either Early Miocene or Oligocene(Lee, 1975, 1978: Bong, 1984: Chun, 1982: Choi et al., 1984: Yun et al., 1990: Yoon, 1982). However, detailed ages of the Tertiary sediments, and their correlations in a basin and between basins are still controversial, since the basins are separated from each other, sedimentary sequence is disturbed and intruded by voncanic rocks, and non-marine sediments are not fossiliferous to be correlated. Therefore, in this work radiometric, magnetostratigraphic, and biostratigraphic data was integrated for the refinement of chronostratigraphy and synopsis of stratigraphy of Tertiary basins of Korea. A total of 21 samples including 10 basaltic, 2 porphyritic, and 9 andesitic rocks from 4 basins were collected for the K-Ar dating of whole rock method. The obtained age can be grouped as follows: $14.8{\pm}0.4{\sim}15.2{\pm}0.4Ma$, $19.9{\pm}0.5{\sim}22.1{\pm}0.7Ma$, $18.0{\pm}1.1{\sim}20.4+0.5Ma$, and $14.6{\pm}0.7{\sim}21.1{\pm}0.5Ma$. Stratigraphically they mostly fall into the range of Lower Miocene to Mid Miocene. The oldest volcanic rock recorded is a basalt (911213-6) with the age of $22.05{\pm}0.67Ma$ near Sangjeong-ri in the Changgi (or Janggi) basin and presumed to be formed in the Early Miocene, when Changgi Conglomerate began to deposit. The youngest one (911214-9) is a basalt of $14.64{\pm}0.66Ma$ in the Haseo basin. This means the intrusive and extrusive rocks are not a product of sudden voncanic activity of short duration as previously accepted but of successive processes lasting relatively long period of 8 or 9 Ma. The radiometric age of the volcanic rocks is not randomly distributed but varies systematically with basins and localities. It becomes generlly younger to the south, namely from the Changgi basin to the Haseo basin. The rocks in the Changgi basin are dated to be from $19.92{\pm}0.47$ to $22.05{\pm}0.67Ma$. With exception of only one locality in the Geumgwangdong they all formed before 20 Ma B.P. The Eoil basalt by Tateiwa in the Eoil basin are dated to be from $20.44{\pm}0.47$ to $18.35{\pm}0.62Ma$ and they are younger than those in the Changgi basin by 2~4 Ma. Specifically, basaltic rocks in the sedimentary and voncanic sequences of the Eoil basin can be well compared to the sequence of associated sedimentary rocks. Generally they become younger to the stratigraphically upper part. Among the basin, the Haseo basin is characterized by the youngest volcanic rocks. The basalt (911214-7) which crops out in Jeongja-ri, Gangdong-myon, Ulsan-gun is $16.22{\pm}0.75Ma$ and the other one (911214-9) in coastal area, Jujon-dong, Ulsan is $14.64{\pm}0.66Ma$ old. The radiometric data are positively collaborated with the results of paleomagnetic study, pull-apart basin model and East Sea spreading theory. Especially, the successively changing age of Eoil basalts are in accordance with successively changing degree of rotation. In detail, following results are discussed. Firstly, the porphyritic rocks previously known as Cretaceous basement (911213-2, 911214-1) show the age of $43.73{\pm}1.05$ 및 $49.58{\pm}1.13Ma$(Eocene) confirms the results of Jin et al. (1988). This means sequential volcanic activity from Cretaceous up to Lower Tertiary. Secondly, intrusive andesitic rocks in the Pohang basin, which are dated to be $21.8{\pm}2.8Ma$ (Jin et al., 1988) are found out to be 15 Ma old in coincindence with the age of host strata of 16.5 Ma. Thirdly, The Quaternary basalt (911213-5 and 911213-6) of Tateiwa(1924) is not homogeneous regarding formation age and petrological characteristics. The basalt in the Changgi basin show the age of $19.92{\pm}0.47$ and $22.05{\pm}0.67$ (Miocene). The basalt (911213-8) in Sangjond-ri, which intruded Nultaeri Trachytic Tuff is dated to be $20.55{\pm}0.50Ma$, which means Changgi Group is older than this age. The Yeonil Basalt, which Tateiwa described as Quaternary one shows different age ranging from Lower Miocene to Upper Miocene(cf. Jin et al., 1988: sample no. 93-33: $10.20{\pm}0.30Ma$). Therefore, the Yeonil Quarterary basalt should be revised and divided into different geologic epochs. Fourthly, Yeonil basalt of Tateiwa (1926) in the Eoil basin is correlated to the Yeonil basalt in the Changgi basin. Yoon (1989) intergrated both basalts as Eoil basaltic andesitic volcanic rocks or Eoil basalt (Yoon et al., 1991), and placed uppermost unit of the Changgi Group. As mentioned above the so-called Quarternary basalt in the Eoil basin are not extruded or intruaed simultaneously, but differentiatedly (14 Ma~25 Ma) so that they can not be classified as one unit. Fifthly, the Yongdong-ri formation of the Pomgogri Group is intruded by the Eoil basalt (911214-3) of 18.35~0.62 Ma age. Therefore, the deposition of the Pomgogri Group is completed before this age. Referring petrological characteristics, occurences, paleomagnetic data, and relationship to other Eoil basalts, it is most provable that this basalt is younger than two others. That means the Pomgogri Group is underlain by the Changgi Group. Sixthly, mineral composition of the basalts and andesitic rocks from the 4 basins show different ground mass and phenocryst. In volcanic rocks in the Pohang basin, phenocrysts are pyroxene and a small amount of biotite. Those of the Changgi basin is predominant by Labradorite, in the Eoil by bytownite-anorthite and a small amount pyroxene.

• Journal of Soil and Groundwater Environment
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• v.14 no.2
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• pp.10-16
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• 2009

Characteristics of natural radioactivity were investigated for soils collected from seven sites of different bed rocks distributed in the Keum River area of Korea by the use of a Gamma-ray spectrometry. Specific activity (SA) and SA ratio (SAR) of typical naturally occurring radioactive nuclide such as $^{226}$Ra, $^{228}$Ac and $^{40}$K were determined for the soil samples. The SA values of $^{226}$Ra, $^{228}$Ac and $^{40}$K in 41 soils of 7 sites are 26.7-485 (74.2 ${\pm}$ 72.2), 30.9-157 (90.7 ${\pm}$ 32.7) and 203-1558 (990 ${\pm}$ 203) Bq/kg, respectively. The SA of $^{226}$Ra has very different values by the soils and the sites. Especially the SA of $^{226}$Ra in a soil sample of Ogcheon site is 485 Bq/kg while most SA of 41 soil samples are < 100 Bq/kg. SA of $^{228}$Ac has a little different values with the soils and sites, however the SA of $^{40}$K has almost constant values in all soil samples. The SAR values of $^{26}$Ra/$^{228}$Ac, $^{226}$Ra/$^{40}$K and $^{228}$Ac/$^{40}$K in 41 soils of 7 sites are 0.343-6.11 (0.865 ${\pm}$ 0.883), 0.0258-0.759 (0.0814 ${\pm}$ 0.1l17) and 0.0373-0.178 (0.0945 ${\pm}$ 0.0373), respectively. The SARs of $^{226}$Ra/$^{228}$Ac and $^{226}$Ra/$^{40}$K have very different values by the soils and the sites, however the SAR of $^{228}$Ac/$^{40}$K has a little difference by the soil and sites.

• Journal of Radiation Protection and Research
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• v.39 no.1
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• pp.7-13
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• 2014

Phosphate rock, phosphogypsum, and products in phosphate processing facility contain naturally occurring radioactive materials (NORM). Therefore, they may give rise to enhanced radiation dose to workers due to inhalation of airborne particulates. Internal dose due to particle inhalation varies depending on particle properties. The objective of the present study was to characterize particle properties at the largest phosphate processing facility in Korea. A cascade impactor was employed to sample airborne particulates at various processing areas in the plant. The collected samples were used for characterization of particle size distribution, particle concentration in the air, and shape analysis. Aerodynamic diameters of airborne particulates ranged 0.03-100 ${\mu}m$ with the highest concentration at the particle size range of 4.7-5.8 ${\mu}m$ (geometric mean = 5.22 ${\mu}m$) or 5.8-9.0 ${\mu}m$ (geometric mean = 7.22 ${\mu}m$). Particle concentrations in the air varied widely by sampling area up to more than two orders of magnitude. The large variation resulted from the variability of mechanical operations and building ventilations. The airborne particulates appeared as spheroids or rough spherical fragments across all sampling areas and sampled size intervals. Average mass densities of phosphate rocks, phosphogypsums, and fertilizers were 3.1-3.4, 2.1-2.6, and 1.7 $gcm^{-3}$, respectively. Radioactivity concentration of uranium series in phosphate rocks varied with country of origin, ranging 94-866 $Bqkg^{-1}$. Among the uranium series, uranium was mostly concentrated on products, including phosphoric acid or fertilizers whereas radium was concentrated on byproducts or phosphogypsum. No significant radioactivity of $^{226}Ra$ and $^{228}Ra$ were found in fertilizer. However, $^{40}K$ concentration in fertilizer was up to 5,000 Bq $g^{-1}$. The database established in this study can be used for the accurate risk assessment of workers due to inhalation of airborne particles containing NORM. In addition, the findings can be used as a basic data for development of safety standard and guide and for practical radiation safety management at the facility.

• The Journal of the Petrological Society of Korea
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• v.8 no.1
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• pp.24-33
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• 1999

Differential Strain Analysis (DSA) was performed to examine the characteristics of microcracks for the granites from two sites, Noeunri and Gunggiri. The results of the DSA are taken every 5 MPa for the first 50 MPa, then every 10 MPa to a pressure of 100 MPa, and then every 15 MPa to a pressure of 250 MPa. Differential strain was measured on core samples in three horizontal directions, using $45^{\circ}$ rosette strain gages, and one vertical direction. The gradients of cumulative crack strain curves in one vertical direction and three horizontal directions differed from one another, indicating anisotropic crack development in the sample. The magnitude of vertical cumulative crack strain was the highest, indicating that the microcracks from the studied rock are generally developed in horizontal direction. Under the pressure of 240 Mpa, vertical cumulative crack strains for samples N-1, N-2, G-1, and G-2 were $74{\times}l0^{-6}~820{\times}l0^{-6},\; 190{\times}l0^{-6}~460{\times}l0^{-6},\; 329{\times}l0^{-6}~836{\times}l0^{-6},\; 833{\times}10^{-6}~1,592{\times}l0^{-6}$, respectively. Under the pressure of 25O MPa, volumetric crack strains for Gunggiri and Noeunri ranged from $1,804{\times}10^{-6}\; to\; 3,936{\times}10^{-6}\; and \;from,\; 1, 125{\times}10^{-6}\; to\; 1,457{\times}10^{-6}$, respectively. Therefore, the amount of microcrackes produced were more distributed in Gunggiri than Noeunri. The ratio of a maximum crack strain to a minimum crack strain was calculated to find the orientations between microcracks and the rift plane of the granites. Generally, the ratio has very high values ranging from 2.42 to 3.43, which suggests most microcracks to be intragranular cracks with the regular orientations. These results indicate that the preferred orientations of microcracks in the granites were almost parallel to the rift plane of the granites.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.3
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• pp.281-290
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• 2018

In order to understand the long-term behavior of radionuclides in granite environments, geochemical behavior characteristics of uranium in granitic host rock of KURT (KAERI Underground Research Tunnel) were investigated by dissolution experiment with different reaction time and solutions. In the dissolution experiment, significantly increased dissolution levels of uranium from granite powder samples were identified during the reaction time of 0~10 days for reaction solutions ($UD-CO_3$ and UD-Bg) containing a large amount of $CO_3{^{2-}}$. On the other hand, significantly increased dissolution levels of uranium were also identified for reaction solutions containing Na and Ca after 60 days. Dissolution of uranium continuously increased in reaction solutions of $UD-CO_3$ ($44.61{\mu}g{\cdot}L^{-1}$), UD-Bg ($41.01{\mu}g{\cdot}L^{-1}$), UD-Na ($26.87{\mu}g{\cdot}L^{-1}$), UD-Ca ($20.26{\mu}g{\cdot}L^{-1}$), UD-CaSi ($17.03{\mu}g{\cdot}L^{-1}$), and UD-Si ($10.47{\mu}g{\cdot}L^{-1}$) in the experimental period of ~270 days. However, after day 270, dissolution of uranium showed a decreasing tendency. This is thought to have occurred because existing uranium in granite samples reached the limit of dissolution by interaction with reaction solutions. Concentrations of dissolved uranium and points of maximum concentration value were found to differ depending on the $CO_3{^{2-}}$ presence in the mixed reaction solution and on the geochemical type of the water. It is estimated that differences in the reaction rate between the granite sample and the reaction solution are due to the influence of dissolved ions in the reaction solution.

• The Journal of the Petrological Society of Korea
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• v.7 no.2
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• pp.69-76
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• 1998

$^{40}Ar/^{39}Ar$ analytical data of hornblende and muscovite separates from granitic rocks in southwestern region of Ogcheon belt shows fellowing tectonic implication, $^{40}Ar/^{39}Ar$ data of 5 samples yield apparent age spectra and $^{37}Ar_{ca}/^{39}Ar_k$ and $^{38}Ar_{CI}/^{39}Ar_k$ plateaus for more than 60% of the $^{39}Ar$ release. Except for HN-100, the $^{36}Ar/^{40}Ar$ versus $^{39}Ar/^{40}Ar$ corelalation diagrams indicate the presence of one distint line. Muscovite of sample PKJ-44 yield flate apparent age plateau for > 60% of the $^{39}Ar_k$ release. In the high temperature steps, the $^{37}Ar_{ca}/^{39}Ar_k$ values are irregular with a correlative increase in $^{38}Ar_{CI}/^{39}Ar_k$, suggesting some Ca and CI rich phase, tapped between the silicate sheet is being argon degassed. The $^{40}Ar/^{39}Ar$ total gas age and the high temperature age of HN-100 is 918.2 Ma and 1360 Ma, respectively. The former affectted by recystallized age of Daebo Orogeny, and the latter indicated age of hornblende closure temperature for cooling stage of amphibole xenolith in granite gneiss. Three rock types of Kwangju granites show about 165 Ma hornblende and muscovite ages with some degassed argon at low temperature steps. These ages of 4 samples indicate also recrystallized age by Daebo Orogeny. In $^{40}Ar/^{39}Ar$ mineral age, Rb/Sr whole age and K/Ar mineral age, discordant ages of southwestern region of Ogcheon belt suggesting cooling rates approaching 3~4$^{\circ}C$/m. y. Such slow cooling rates can be produced by uplift rate of 100m/m.y. or slightly slower than isothem-migration rate derived from the hornblende samples. We conclude that the strongest Orogeny and igneous activity of southwestern region of Ogcheon belt are middle proterozoic era (about 1360 Ma) and middle Jurassic period (about 165 Ma).

• The Journal of the Petrological Society of Korea
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• v.7 no.2
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• pp.111-131
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• 1998

The migmatitic gneiss in the Odesan Gneiss Complex has small amount of quartzite, amphibolite and marble and the Kuryong Group which contact with migmatitic gneiss unconformitly, also contains some amphibolite. Preview studies of this area had regarded that the amphibolites contact with marble had been produced by metasomatism from the pelitic and calcareous sediments mixtures, but the amphibolite is reinterpreted as igneous origin. $SiO_2$ content of the amphibolite is 45.9~52.7 wt%, which corresponds to basaltic composition. MgO content has narrow range (4.6~6.87 wt%) and major and trace element are plotted against MgO,$TiO_2, P_2O_5$, Hf, Zr are reduced and Cr and Ni are increased their content with increasing MgO. This phenomenon indicates that the basaltic magma as the protolith of the amphibolite had frationated with the crystallization of the pyroxene and/or olivine. REE pattern has smoothly decrease from LREE to HREE. Eu/Eu(0.83~1.19) show the flat Eu anomaly, which indicate small fractional crystallization of plagioclase. HREE is enriched in the garnet-bearing amphibolites. Several discrimination diagram for the basaltic magma show that the amphibolite of the study area is originated tholeiitic basaltic magma indicating continental rift environment. Due to determine the metamorphic condition garnet-hornblende geothermometry and hornblende-plagioclase geobarometry are used. Peak metamorphic temperature range of the amphibolite $788~870^{\circ}C$ and is deduced toward the northeastern part. The calculated temperature from the amphibolite has slightly higher than the temperature of the metapelites but the trend of metamorphic grade which decrease from western to eastern part progradly is similar to each other. The metamorphic pressure calculated by garnet- hornblede-plagioclase geobarometry is 4~5kb. But ilmenite-plagioclase pair enclosed in garnet show 8 kb at $700^{\circ}C$ by garnet-ilmenite-rutile-plagioclase geobarometery. The zonal profile of garnet in sample 84 shows the bell-shape profile, which grossular content decreases whereas pyrope content increases progressively. This means that the amphibolite has undergone the clockwise P-T-t path which is shown in the migmatitic gneiss of the Odesan Gneiss Complex.

• Korean Journal of Heritage: History & Science
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• v.50 no.4
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• pp.122-147
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• 2017

The Jungsandong sites are distributed across quartz and mica schist formations in Precambrian, and weathering layers include large amounts of non-plastic minerals such as mica, quartz, felspar, amphibole, chlorite and so on, which form the ground of the site. Neolithic pottery from Jungsandong exhibits various brown colors, and black core is developed along the inner part for some samples, and sharp comb-pattern and hand pressure marks can be observed. Their non-plastic particles have various composition, size distribution, sorting and roundness, so they are classified into four types by their characteristic mineral compositions. I-type (feldspar pottery) is including feldspar as the pain component or mica and quartz. II-type (mica pottery) is the combination of chloritized mica, talc, tremolite and diopside. III-type (talc pottery) is with a very small amount of quartz and mica. IV-type (asbestos pottery) is containing tremolite and a very small amount of talc. The inner and outer colors of Jungsandong pottery are somewhat heterogeneous. I-type pottery group shows differences in red and yellow degree, depending on the content of feldspar, and is similar to III-type pottery. II-type is similar to IV-type, because its red degree is somewhat high. The soil of the site is higher in red and yellow degree than pottery from it. The magnetic susceptibility has very wide range of 0.088 to 7.360(${\times}10^{-3}$ SI unit), but is differentiated according to minerals, main components in each type. The ranges of bulk density and absorption ratio of pottery seem to be 1.6 to 1.7 and 13.1 to 26.0%, respectively. Each type of pottery shows distinct section difference, as porosity and absorption ratio increase in the order as follows: I-type (organic matter fixed sample) < III-type and IV-type < I-type < II-type (including IV-type of IJP-15). The reason is that differences in physical property occur according to kind and size of non-plastic particles. Although Jungsandong pottery consists of mixtures of various materials, the site pottery has a geological condition on which all mineral composition of Jungsandong pottery can be provided. There, it is thought that raw materials can be supplied from weathered zone of quartz and mica schist, around the site. However, different constituent minerals, size and rock fragments are shown, suggesting the possibility that there can be more raw material pits. Thus, it is estimated that there may be difference in clay and weathering degree.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.1
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• pp.73-94
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• 2023

We carried out the sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb age dating and whole-rock geochemical analysis of granitoids and felsic porphyries in the Ssangyong Valley, Yongchu Valley, and Mungyeong Saejae geosites in the Mungyeong Geopark. The igneous rocks crop out in the western, northwestern and central parts of the Mungyeong city area, respectively, and intruded (meta)sedimentary successions of the Ogcheon Metamorphic Belt, Cambro-Ordovician Mungyeong Group and Jurrasic Daedong Group. The U-Pb isotopic compositions of zircon from two felsic porphyries and one granite samples in the Ssanyeong Valley yielded the Cretaceous intrusion ages of 93.9±3.3 Ma (tσ), 95.1±4.0 Ma (tσ) and 94.4±2.0 Ma (tσ), respectively. On the other hand, a felsic dike sample and a granite in the Yongchu Valley and a porphyritic granite in the Mungyeong Saejae had intrusion ages of 90.2±2.0 Ma (tσ), 91.0±3.0 Ma (tσ) and 88.6±1.5 Ma (tσ), respectively. Based on the average standard error calculated in combination with results of previous studies in this area (Lee et al., 2010; Yi et al., 2014; Aum et al., 2019), the geochronological results show that spatial variation in intrusion age of ~5 Myr between the Ssangyong (94.5±0.2 Ma) and Yongchu Valleys (89.7±0.4 Ma) is apparent. The geochemical compositions of major and trace elements in the samples showed an affinity of typical post-orogenic granite, indicating their petrogenesis during the late stage of Early Cretaceous magmatic activity possibly in association with subduction events of the Izanagi Plate.