• Economic and Environmental Geology
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• v.32 no.6
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• pp.561-573
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• 1999

Mesothermal gold deposits of the Heungdeok, Daewon and Ilsaeng mines in the Youngdong area occur in fault shear zones in Precambrian metamorphic rocks of central Sobaegsan Massif, Korea, and formed in single stage of massive quartz veins (0.3 to 3 m thick). Ore mineralogy is simple, consisting dominantly of pyrrhotite, sphalerite and galena with subordinate pyrite, chalcopyrite, electrum, tetrahedrite and native bismuth. Fluid inclusion data indicate that hydrothermal mineralization occurred at high temperatures (>240$^{\circ}$ to 400$^{\circ}$C) from $H_{2}O-CO_{2}(-CH_{4})$-NaCI fluids with salinities less than 12 wt. % equiv. NaC!. Fluid inclusions in vein quartz comprise two main types. These are, in decreasing order of abundance, type I (aqueous liquid-rich) and type II (carbonic). Volumetric proportion of the carbonic phase in type II inclusions varies widely in a single quartz grain. Estimated $CH_4$ contents in the carbonic phase of type II inclusions are 2 to 20 mole %. Relationship between homogenization temperature and salinity of fluid inclusions suggests a complex history of fluid evolution, comprising the early fluid's unmixing accompanying $CO_2$ effervescence and later cooling. Estimated pressures of vein filling are at least 2 kbars. The ore mineralization formed from a magmatic fluid with the ${\delta}^{34}S_{{\Sigma}S}$, ${\delta}^{18}O_{water}$ and ${\delta}D_{water}$ values of -2.1 to 2.2$\textperthousand$, 4.7 to 9.3$\textperthousand$ and -63 to -79$\textperthousand$, respectively. This study validates the application of a magmatic model for the genesis of mesothermal gold deposits in Youngdong area.

• The Journal of the Petrological Society of Korea
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• v.5 no.2
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• pp.168-187
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• 1996

In the study area Uanggunbong-Samgunri area), Precambrian metamorphic complex, (Taebacksan gneiss complex, Hyundong gneiss complex, and Taebacksan schist complex) had undergone three different regional metamorphisms at least before Paleozoic. The Paleozoic sediments in the study area also had undergone three different metamorphisms at least. The first is low pressure type regional metamorphism, the second is low pressure type contact metamorphism due to the intrusion of Chunyang granite, and the last is medium pressure type metamorphism caused by thrust in south of Janggunbong area. The first metamorphism formed the prevailing metamorphic zones in the Paleozoic metasediments and the metamorphic grade of the first regional metamorphism increases from the chloritoid zone, through the staurolite zone, garnet zone, staurolite+biotite zone, and to the andalusite+biotite zone. The second metamorphism affected both Pre-Cambrian and Paleozoic metasediments located close to the Chunyang granite. The effect of the contact metamorphism is restricted to the very narrow zone around the granite. The third metamorphism that produced kyanite, is restricted to the very narrow region near the thrust fault in the south of Janggunbong with an E-W trend.

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.179-190
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• 2004

Precambrian metamorphic rocks of Yeongyang-Uljin area, which is located in the eastern part of Sobaegsan Massif, Korea, are composed of Pyeonghae, Giseong, Wonnam Formations and Hada leuco granite gneisses. These show a zonal distribution of WNW-ESE trend, and are intruded by Mesozoic igneous rocks and are unconformably overlain by Mesozoic sedimentary rocks. This study clarifies the deformation history of Precambrian metamorphic rocks after the formation of gneissosity or schistosity on the basis of the geometric and kinematic features and the forming sequence of multi-deformed rock structures, and suggests that the geological structures of this area experienced at least four phases of deformation i.e. ductile shear deformation, one deformation before that, at least two deformations after that. (1) The first phase of deformation formed regional foliations and WNW-trending isoclinal folds with subhorizontal axes and steep axial planes dipping to the north. (2) The second phase of deformation occurred by dextral ductile shear deformation of top-to-the east movement, forming stretching lineations of E-W trend, S-C mylonitic structure foliations, and Z-shaped asymmetric folds. (3) The third phase deformation formed I-W trending open- or kink-type recumbent folds with subhorizontal axes and gently dipping axial planes. (4) The fourth phase deformation took place under compression of NNW-SSE direction, forming ENE-WSW trending symmetric open upright folds and asymmetric conjugate kink folds with subhorizontal axes, and conjugate faults thrusting to the both NNW and SSE with drag folds related to it. These four phases of deformation are closely connected with the orientation of regional foliation in the Yeongyang-Uljin area. 1st deformation produced regional foliation striking WNW and steeply dipping to the north, 2nd deformation locally change the strike of regional foliation into N-S direction, and 3rd and 4th deformations locally change dip-angle and dip-direction of regional foliation.

• Journal of the Korean earth science society
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• v.22 no.6
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• pp.528-547
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• 2001

The blastoporphyritic granite gneiss (BPGN) including much alkali-feldspar megacrysts occurs in Jiri mountains area, southwestern part of Sobaegsan massif, Korea. The BPGN is formed gneiss complexes with other gneisses in Precambrian. The BPGN was named as porphyroblastic gneiss with porphyroblasts of alkali-feldspar megacrysts by other researchers, but the BPGN includes of euhedral alkali-feldspars (microcline), and the boundary with the granitic gneiss represents sharp contact as intrusive relationship. The BPGN mainly composes of alkali-feldspar megacrysts, quartz, plagioclase, K-feldspar and biotite some almandine and accessary minerals are muscovite, chlorite, apatite, zircon and opaques. The alkali-feldspar is microcline with perthitic texture. An content of plagioclases show 30 to 40. Biotites occur two type, one is Brown biotite which shows compositional ranges of Mg/Fe+Mg ratios from 0.38 to 0.52, the other is Green Bt. which is retrograde product. Camels to be various sizes and shapes have composition of almandine with 73 to 80 mole percent, but represent retrogressive zoning from core (X$_{pyr}$: 15.9${\sim}$20.8) to rim (X$_{pyr}$:13.7${\sim}$15.9) to be evidence of retrograde metamorphism. Megacrysts of alkali-feldspar in the BPGN show rectangular shape of euhedral and some become ellipsoidal or spheroidal in shape and the average size up to 20 cm long. The megacryst includes of biotite, plagioclase and quartz, and rarely euhedral apatite as inclusions. In petrochemistry the BPGN represents granodiorite composition, characteristics of peraluminous S-type granitoid and calc-alkaline features.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.623-633
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• 1995

The Beonam deposits which is located in south-western part of Sobaeksan massif are emplaced along $N20{\sim}30^{\circ}E$ trending fissures in Precambrian Sobaeksan gneiss complex. Surrounding granites are inferred to be differentiated and formed from calc-alkaline magma which was generated from remelting or partial melting of the crustral material having igneous composition. The Sr isotope data of ore minerals showing significantly low initial Sr value relative to those of surrounding granite batholiths suggest that the ore-bearing fluid formed the Beonam Au-Ag mine are isotopically distinct from those of the wall rocks, and it indicates that there is no evidence of genetic relationship between ore-bearing fluids and surrounding granites, although further study should be needed. The results of paragenetic studies suggest three stages of hydrothermal mineralization; stage I: base-metal sulfides stage, stage II: late base-metal sulfides, electrum and silver-bearing sulfosalts stage, stage III: minor silverbearing minerals, barren quartz and carbonates stage. The temperature, salinity and pressure of the Beonam deposits estimated from mineral assemblage, chemical composition, fluid inclusion and sulfur isotope geothermometry are as follows; stage I: $200{\sim}315^{\circ}C$, 3.5~6.5 NaCl eq. wt%, 0.28~0.61 Kbar, stage II: $150{\sim}235^{\circ}C$, 4.5~7.4 NaCl eq. wt%, 0.11~0.15 Kbar. The estimated oxygen and sulfur fugacity during first stage mineralization, based on phase relation of associated minerals, range from $10^{35.1}{\sim}10^{-39.7}$ atm. and $10^{-11.0}{\sim}10^{-13.4}$ atm., respectively. All these evidences suggest that the Beonam deposits are polymetallic meso-epithermal ore deposits.

• The Journal of the Petrological Society of Korea
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• v.3 no.1
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• pp.94-108
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• 1994

The Precambrian granite, and the Yuli group and the Hyeondong gneisss complex are studied to unravel the metamorphic history of the northeastern Sobaeksan massif. The Hongjesa granite, emplaced at 650-$700^{\circ}C$ and $3{\pm}1$ kbar, has been altered at 310-$568^{\circ}C$. Not only the chloritization of biotite but also the sericitization and saussuritization of plagioclase occur at the subsolidus stage. Biotites of the Hongjesa granite vary in their Al, Fe and Mg contents through dioctahedral and tschermakitic substitutions during the subsolidus stage. Secondary muscovites from biotite and feldspars are enriched in their Si and Mg+Fe contents through tschermakitic and trictahedral substitutuions. The metamorphic pressures and temperatures estimated from the Hyeondong gneiss complex are 3.6-6.6 kbar and 593-$718^{\circ}C$, respectively. Local migmatization producing the cordierite-bearing assemblage occurs in the Hyeondong gneiss complex. The Gibbs' method applied to the assemblage of garnet+biotite+plagioclase+quartz in banded gneiss suggests a complex P-T history of the Hyeondong gneiss complex.

• The Journal of the Petrological Society of Korea
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• v.8 no.3
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• pp.183-202
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• 1999

The Sobeaksan Gneiss Complex in the Punggi area is composed of mainly mignatitic gneiss, porphyroblastic gneiss, garnet granitic gneiss and biotitie granitic gneiss. Metamorphic grade increase gradually from the amphibolite facies of northwestern part to the granulite facies of southwestern part in the study area. Representative mineral assemblage in the amphibolite facies is biotite-muscovite-K-feldspar-plagioclase$\pm$garnet$\pm$epidote, needle shape or fibrous sillimanite occur in transitional zone from the amphibolite facies to the granulite facies. In the granulite facies, the garnet-Opx granulite shows garnet-orthopyroxene-biotite-plagioclase, the metabasite shows clinopyroxene-plagioclase$\pm$hornblende$\pm$orthopyroxene$\pm$garnet and the migmatitic gneiss shows garnet-biotite-sillimanite-cordierite$\pm$spinel as representative mineral assemblage. Retrograde metamorphism after the granulite facies metamorphism made corindum and andalusite in the migmatitic gneiss and the thin layer garnet between clinopyroxene and plagioclase in the metabasites. The peak P-T conditions of the migmatitic gneiss and the garnet-Opx granulite are $916^{\circ}C$/6.6 kb and $826^{\circ}C$/6.3 kb, respectively. The P-T condition of biotite and plagioclase inclusion, which indicates the progressive condition of the granulie facies, within garnet is $866^{\circ}C$/7.5 kb and that of rim composition of garnet and biotite is $726^{\circ}C$/4.6 kb, which infer the clockwise P-T path of the granulite facies metamorphism. The temperatures caculated by the rim composition of garnet and biotite in the migmatitic gneiss and garnet granitic gneiss have a wide range of $556-741^{\circ}C$, which indicate that the retrograde metamorphism after the granulite facies metamorphism has effected differently. It is difficult to determine the P-T condition of the biotite granitic gneiss because less occurrence and higher spessartine content of garnet. The P-T condition of the thin layered garnet between clinopytoxene and plagioclase in the metabasite is $635-707^{\circ}C$/4.1-5.3 kb. This texture indicates the isobaric cooling(IBC) condition of the retrogressive metamorphism. As a result, the metamorphic evolution of the Punggi area has undergone the isobaric cooling after the granulite facies metamorphism which has undergone the clockwise P-T path.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.139-151
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• 2018

The Songgang-ri area, Cheongsong-gun, which is located in the Sobaeksan province of Yeongnam Massif near the southwestern boundary of Yeongyang subbasin of Gyeongsang Basin, consists of age unknown metamorphic rocks (banded gneiss, granitic gneiss, limesilicates) and age unknown igneous rock (granite gneiss) which intrudes them. This paper researched the geological structures of the Songgang-ri area from the geometric and kinematic features and the developing sequence of multi-deformed rock structures in the geological outcrops exposed about 170 m along the riverside of Yongjeoncheon in the eastern part of Songgang village, Songgang-ri. In the Songgang-ri geological outcrops are recognized three times (Fn, Fn+1, Fn+2) of folding, three times (Dk-I, Dk-II, Dk-III) intrusion of acidic dykes, one time of faulting, which are different in deformation and intrusion timing each other. These geological structures are at least formed by five times (Dn, Dn+1, Dn+2, Dn+3, Dn+4) of deformation. The Dn deformation is recognized by Fn fold which axial surface is parallel to the regional foliation. The Dn+1 intruded the (E)NE trending Dk-I dyke in the earlier phase and formed the NW trending Fn+1 fold in the later phase under compression of (E)NE-(W)SW direction. There are tight, isoclinal, intrafolial folds, boudinage, ${\sigma}$- or ${\delta}$-type boudins, asymmetric fold, C' shear band as the major deformed rock structures. The Dn+2 intruded the (N)NW trending Dk-II dyke in the earlier phase and formed NE trending Fn+2 fold in the later phase under compression of (N)NW-(S)SE direction. There are open fold and folded boudinage as those. The Dn+2 intruded the Dk-III dyke which cuts the Dk-I and Dk-II dykes and the axial surface of Fn+2 fold. The Dn+3 formed the left-handed reverse oblique-slip fault of NNE trend in which hanging wall moves into the SSE direction. Considering in that such five times of deformation recognized in the Songgang-ri geological outcrops are closely connected to the distribution and geological structure of the constituents in the more regional area as well as Songgang-ri area, the research result is expected to play a great data in clarifying and understanding the geological structure and its development process of the surrounding and boundary constituents of the Yeongnam Massif and Gyeongsang Basin.

• Economic and Environmental Geology
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• v.51 no.5
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• pp.409-428
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• 2018

Yeongdong area is located on the border zone between Precambrian Yeongnam massif and central southeastern Ogcheon metamorphic belt, in which Cretaceous Yeongdong sedimentary basin exists. Main geology in this area consists of Precambrian Sobaeksan gneiss complex, Mesozoic igneous and sedimentary rocks and Quaternary alluvial deposits. Above this, age-unknown Ogcheon Supergroup, Paleozoic sedimentary rocks and Tertiary granites also occur in small scale in the northwestern part. This study focuses on the link between the various geology and Rn concentrations in groundwater. For this, twenty wells in alluvial/weathered zone and sixty bedrock aquifer wells were used. Groundwater sampling campaigns were twice run at wet season in August 2015 and dry season in March 2016. Some wells placed in alluvial/weathered part of Precambrian metamorphic rocks and Jurassic granite terrains, as well as Cretaceous porphyry, showed elevated Rn concentrations in groundwater. However, detailed geology showed the distinct feature that these high-Rn groundwaters in metamorphic and granitic terrains are definitely related to proximity of aquifer rocks to Cretaceous porphyry in the study area. The deeper wells placed in bedrock aquifer showed that almost the whole groundwaters in biotite gneiss and schist of Sobaeksan gneiss complex and in Cretaceous sedimentary rocks of Yeongdong basin have low level of Rn concentrations. On the other hand, groundwaters occurring in rock types of granitic gneiss or granite gneiss among Sobaeksan gneiss complex have relatively high Rn concentrations. And also, groundwaters occurring in the border zone between Triassic Cheongsan granites and two-mica granites, and in Jurassic granites neighboring Cretaceous porphyry have relatively high Rn concentrations. Therefore, to get probable and meaningful results for the link between Rn concentrations in groundwater and surrounding geology, quite detailed geology including small-scaled dykes or vein zones should be considered. Furthermore, it is necessary to take account of the spatial proximity of well location to igneous rocks associated with some mineralization/hydrothermal alteration zone rather than in-situ geology itself.

• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.153-177
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• 2013

To get the various data on geological information, distributional ratios and characteristics of constituent rocks with geologic ages and rock types were obtained by ArcGIS 10.1 program, digital geologic and geomorphic maps of 1:250,000 scale in Jeonnam and Gwangju areas. In the Jeonnam area, geologic ages can be largely divided into 7, in which their distribution ratios show decreasing trends in the order of Cretaceous, Precambrian, Jurassic, Quaternary, Age-unknown, Carbonifeorus-Triassic and Triassic, and the former fours make the most prevailing ratios of 94.80%. Rock types in the area can be assorted into 57 ones, in which major 7 ones occupy the dominant ratio of 71.68%. Among them, Kav (acidic volcanics+rhyolite and rhyolitic tuff) show much more distribution ratios than the others. It shows more aspects distributed in north, west, middle, east and south parts, especially in Sinan-Mogpo-Yeongam of west and Haenam of south parts in the area, respectively. On the other hand, geological ages in Gwangju area can be largely divided into 5, in which their distribution ratios show decreasing trends in the order of Jurassic, Quaternary, Cretaceous, Precambrian and Age-unknown, and the former fours occupy almost the whole ratio of 98.95%. Rock types in the area are 12 ones, in which major four ones make up the dominant value of 91.30%. Among them, Jurassic granites of the most dominant value are mostly occupied in the southwest-northeast part of the area. Next dominative Quaternary alluvium is mostly developed along the Yeongsan river, the Hwangryong river and their channel junction. And Yongdu and Donggye plains are well developed around the Yeongsan riverline, and channel junction of the Yeongsan and Hwangryong rivers in the area, respectively.