• Economic and Environmental Geology
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• v.9 no.1
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• pp.27-43
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• 1976

The flourite in Hwacheon, Hwanggangri and Keumsan district are major fluorite producing areas in Korea. The fluorite deposits of Hwacheon district are wholly fissure filling hydrothermal veins embedded in Precambrian gneiss and schists and Jurassic granites. Also some fluorite deposits are emplaced in felsite whose age is unknown. Emplacement of most fluorite veins of the district are controlled by EW fracture system. Fluorites are generally accompanied to chalcedonic quartz and also kaolinite, montmorillonite, dickite and calcite in parts. Vertical and lateral mineral zonings are not distinct. The fluorite deposits in the Hwanggangri district are wholly embedded in limestone and other calcareous sediments of Paleozoic Yeongweol Group. Most of the fluorite deposits belong to one of two categories which are steeply. dipping veins and gently dipping replacement deposits adjacent to Late Cretaceous(83-90mys) granite bodies. The strikes of fluorite veins of Hwanggangri district mostly occupy the fractures of $N30^{\circ}-40^{\circ}E$ and $N30^{\circ}-40^{\circ}W$ system. Fluorites are accompanied to calcite, milky quartz, chalcedonic quartz, and also montmorillonite, kaolinite in parts. But in some deposits, scheelite, various sulfide minerals and barite are accompanied. Emplacement of fluorite deposits are largely controlled by lithology and structures of this district. In some deposits fluorite veins gradate to scheelite veins and also telescoping of the mineral zones are found in this district. In the Keumsan district, fissure-filled fluorite veins and replacement deposits are mostly emplaced in limestone of Paleozoic Yeongweol Group, late Cretaceous quartz-porphyry, granite and sandstone. Some deposits are emplaced in Precambrian metasediments. Mineralogy and other characteristics of the deposits in this district is similar to those of Hwanggangri district. Fluid inclusion studies reveal the difference of salinities, $CO_2$ contents of ore fluid and temperatures during fluorite mineral deposition in the these districts. In Hwacheon district, ore-fluids were comparatively dilute brine and low $CO_2$ content. Filling temperatures ranges $104^{\circ}C$ to $170^{\circ}C$. In the Chuncheonshinpo mine, most deeply exploited one in this district, salinitles range 0.5-2. 2wt. % NaCl and filling temperatures range from $116^{\circ}C$ to $143^{\circ}C$. In the Hwanggangri district, ore fluids were complex and filling temperature ranges very widly. In the contact metasomatic fluorite deposits, ore fluid were NaCl rich brines with moderate $CO_2$ content and filling temperatures range from $285^{\circ}C$ to above $360^{\circ}C$. Fluids inclusions in tungsten and sulfide minerals bearing fluorite veins show high $CO_2$ content up to 31wt. %. Filling temperature ranges from $101^{\circ}C$ to $310^{\circ}C$. Fluids inclusions In mainly fluorite bearing veins were more dilute brine and low $CO_2$ contents. Filling temperatures range from $95^{\circ}C$ to $312^{\circ}C$. Filling temperature of fluid inclusions of Keumsan district are between $95^{\circ}C$ and $237^{\circ}C$. Data gathered from geologic, mineralogic and fluid inclusion studies reveal that fluorite mineralization in H wacheon district proceeded at low temperature with dilute brine and low $CO_2$ content. In Hwangganri district, fluorite mineralization proceeded by several pulse of chemically distinct ore fluids and formed the mineralogically different type of deposits around cooling granite pluton which emplaced comparatively shallow depth.

• Economic and Environmental Geology
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• v.16 no.3
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• pp.163-221
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• 1983

Main aspects of this study are to clarify geochronology and petrogenetic processes of the so-called Hongjesa granite, which is a member of various intrusive rocks exposed in the northeastern part of the Ryongnam Massif, one of the Precambrian basements of South Korea. In this study, the Hongjesa grainte is divided into four rock units based on the geologic age, mineralogical and chemical constituents, and texture: the Precambrian Hongjesa granite gneiss (Hongjesa granite Proper) and leucogranite gneiss, the Paleozoic gnessic two mica granite, and the Jurassic muscovite granite. The Hongjesa granite gneiss is identified by its grayish color, slight foliation, and porphyroblastic texture. The leucogranite gneiss is distinct by its light gray color, sand medium to coarse grained texture. The gneissic two mica granite is distinguished from others by its strong foliation, containing gray-colored feldspar phenocrysts with biotite and muscovite in varying amounts. The muscovite granite occurs as a small stock containing feldspar phenocrysts along margin of the stock. These granitic rocks vary widely in composition, reflecting the facts that they partly include highly metamorphosed xenolith and schlierens as relics of magmatic and anatectic processes. In particular, grayish porphyroblasts of microcline perthite is characteristic of the Hongjesa granite gneiss, whereas epidote and garnet occur in both the Hongjesa granite gneiss and leucogranite gneiss. These minerals are considered to be formed by potassic metasomatism and contamination of highly metamorphosed rocks deeply buried under the level of the Hongjesa granite emplacement. The individual synchronous granitic rocks plotted on Harker diagram show mostly similar trends to the Daly's values. The plots of the Hongjesa granite gneiss and gneissic two mica granite concentrate near the end part of the calc-alkalic rock series on the AMF diagrams, whereas those of the leucogranite gneiss and muscovite granite indicate the trend of the Skaergaard pluton. These granitic rocks plotted on a Q-Ab-Or diagram (petrogeny's residua system) fall well outside the trough of the system. This can be attributed to the potassic matasomatism of these rocks. On the ACF diagram, these rocks appear to be dominantly I-type prevailing over S-type. The K-Ar ages, obtained from a total of 7 samples of the leucogranite gneiss, gneissic two mica granite, muscovite granite, porphyritic alkali granite, and rhyolitic rock, in addition to the Rb/Sr ages of the Hongjesa granite gneiss by previous workers, permit the rock units to be arranged in the following chronological order: The middle Proterozoic Hongjesa granite gneiss (1714-1825 m.y.), the upper proterozoic leucogranite gneiss (875-880 m. y.), the middle Paleozoic gneissic two mica granite (384 m. y.) the upper Jurassic muscovite granite (147 m. y.), the Eocene alkali granite (52 m. y.), and the Eocene rhyolitic rock (45 m. y.). From the facts and data mentioned above, it is concluded that the so-called Hongjesa granite is not a single granitic mass but is further subdivided into the four rock units. The Hongjesa granite gneis, leucogranite gneiss, and gneissic two mica granite are postulated to be either magmatic or parautochtonous, intrusive, and the later muscovite granite is to be magmatic in origion.

• Economic and Environmental Geology
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• v.17 no.3
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• pp.215-230
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• 1984

Petrological, paleomagnetic, geomorphological and structural studies on the southern part of, so called, Chugaryeong rift valley, have been carried out in order to clarify the nature of the rift valley. Three stages of volcanic activities characterized by Jijangbong acidic volcanic rocks and tholeiitic and andesitic basalt of Cretaceous age(?), and Jongok Quaternary olivine basalt occurred along the Dongducheon fault line. Jijangbong acidic volcanic rocks distributed in the central part of the studied area consist of rhyodacite, acidic tuff and tuff breccia, which are bounded by Dongsong fault on the east and Daegwangri fault on the west. The Jongok basalt differs from those of Ulrung and Jeju islands in mineralogy, chemical composition and differentiation. Jongok basalt distributed along the Hantan river dilineates the vesicles curved toward downstream direction and increment of numbers and thickness of lava flow toward upstream direction. These facts suggest that lava flowed from upstream side of the river. Rectangular drainage patterns also support the presence of the Dongducheon, Pocheon, Wangsukcheon and Kyonggang faults which were previously known. LANDSAT image, however, does not show any lineaments which could be counted as a graben or rift valley. Displacement of Precambrian quartzite and Jurassic Daedong supergroup along the southwestern extension of the Dongducheon fault shows the right lateral movement. The Paleomagnetic study of the tholeiitic and andesitic basalts from Baegeuri, Jangtanri and Tonghyeonri located at 2. 3km east, 0km east, and 1.5km west of Dongducheon fault respectively shows that their VGP(Virtual Geomagnetic Pole) being to intermediate geomagnetic field of short duration which suggests that they formed in almost same period. Mean VGP of Jongok basalt is located 82.4N and 80.6E. This is in good coincidence with worldwide VGP of Plio-Pleistocene indicating that Jongok basalt was extruded during Plio-Pleistocene epoch, and suggesting that the studied area has been tectonically stable since then. From the present study, the tectonic episode of the region is concluded as following three stages. 1. The 1st period is worked by the Daebo orogeny of Jurassic during which granodiorite was intruded in Precambrian basement. 2. The 2nd period is the time when right lateral strike-slip fault of NNE-SSW direction was formed probably during late Cretaceous to Paleogene and the Jijangbong acidic volcanic rocks and the older basalts were extruded. 3. The 3rd period is the time when the fault was rejuvenated during Pliocene or Pleistocene accompanied by the eruption of Jongok basalt. As a conclusion, geologic structure of the studied area is rather fault line valley than graben or rift valley, which is formed by differential erosion along the Dongducheon fault suggesting a continuation of the Sikhote-Alin fault. The volcanic rocks including the Jijangbong acidic rocks, tholeiitic-andesitic basalt and olivine basalt are associated with this fault line.

• Journal of the Korean Society of Groundwater Environment
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• v.7 no.3
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• pp.116-124
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• 2000

Geochemical and isotopic analyses were carried out to investigate hydrochemical characteristics, source of carbon species in the carbonated waters in South Korea. Most Korean carbonated waters from different geologic settings are characterized by a Ca-HCO$_3$type with a relatively low pH range from 5.3 to 6.3 (avg. 6.0). The concentrations of cations and anions in the carbonate waters are in the order of Ca$^{2＋}$>Na$^{＋}$>Mg$^{2＋}$>Si$^{4＋}$>Fe$^{2＋}$>K$^{＋}$ and HCO$_3$$^{－}$>SO$_4$$^{2－}$>Cl$^{－}$, respectively. The HCO$_3$$^{－}$ ion is more enriched in the carbonated water from the sedimentary rock and granitic rock of Mesozoic age in the Gyungsang basin(GII) and the Precambrian metamorphic rock and Jurassic granitic rocks of the Gyunggj massif in the Gangwon province(GⅠ) than those of the meta-sedimentary rock and granite in the Ogcheon zone(GⅢ). Based on the oxygen and hydrogen isotopic data, the carbonated waters are derived from the meteoric water, showing apparent latitude and altitude effects. The $delta$$^{13}$C values of carbon species in the carbonated water are in between -6.23 and 0.0 $textperthousand$, suggesting inorganic source of carbon originated from the carbonate mineral and carbonate rock in the aquifer.

• Economic and Environmental Geology
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• v.52 no.5
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• pp.409-425
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• 2019

Marine terraces, a step-like landform, are important geologic markers that provide tectonic information during the Quaternary Period. Marine terraces are well developed along all coastlines(East, West, and South) of the Korean Peninsula, those along the East coastline are the most distinctive. The marine terraces of the East coastline are classified into 4-6 flights that are several meters or several tens of meters above the present sea level. It is believed that these terraces, except for the lowest one, were formed in the middle Pleistocene. In the base of the OSL age dating results and Blake excursion events of magnetostratigraphy, the $2^{nd}$ and $3^{rd}$ terraces are correlated to the last interglacial stage. Considering the marine terraces linked to a sea-level curve of the Pleistocene, it is thought that regional tectonic movements have uplifted the East coastal area since the middle Pleistocene. Besides, former shorelines of each terrace have varied elevations from Gangreung to Busan bay, which can be divided into four regions, namely, Gangreung-Yonghanri(I), Homikot-Najung(II), Najung-Bangeojin(III), and Waesung-Busan Bay(IV). The former shorelines of each terrace at both Gangreung-Yonghanri(I) and Najung-Bangeojin(III) are higher than those in the other two regions, due to block movements by regional faults such as the Ocheon Fault or its subsidiaries, the Gampo Lineament and Ulsan Fault. Uplift rate of the East coast ranges from 0.2 m/ky to 0.3 m/ky, but each region shows different uplift rate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.1
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• pp.35-44
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• 2022

The V_S30 map is used as a key variable for site amplification in the ShakeMap, which predicts ground motion at any site. However, no V_S30 map considering Korean geology and geomorphology has been developed yet. To develop a proxy-based V_S30 map, we used 1,101 V_S profiles obtained from a geophysical survey and collected proxy layers of geological and topographical information for the Korean Peninsula. Then, V_S30 prediction models were developed using linear regression analysis for each geological age considering the distribution of V_S30. As a result, models depending on geomorphology were suggested per each geologic group, including Quaternary, Fill, Ocean, Mesozoic group and Precambrian. Resolution of map is doubled from that of V_S30 map by U.S. Geological Survey (USGS). Standard deviation of residual in natural log of proxy-based V_S30 map is 0.233, whereas standard deviation of slope-based USGS V_S30 map is 0.387. Therefore, the proxy-based V_S30 map developed in this study is expected to have less uncertainty and to contribute to predicting more accurately the ground motion amplitude.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.153-171
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• 2018

This study focuses on the investigation of geologic distribution and stratigraphy in the eastern part of Yeongdeok-gun, based on Lidar imaging, detailed field survey, microscopic observations, SHRIMP and LA-MC-ICPMS U-Pb age dating, and a new geological map has been created. The stratigraphy of the study area is composed of the Paleoproterozoic metamorphic rocks consisting of banded gneisses of sedimentary origin and schists ($1841.5{\pm}9.6Ma$) of volcanic origin, Triassic Yeongdeok plutonic rocks ($249.1{\pm}2.3Ma$) and Pinkish granites ($242.4{\pm}2.4Ma$), Jurassic Changpo plutonic rocks ($193.2{\pm}1.9Ma{\sim}188.8{\pm}2.0Ma$) and Fine-grained granites ($192.9{\pm}1.7Ma$), Formations [Gyeongjeongdong Fm, Ullyeonsan Fm. (~108 Ma), Donghwachi Fm.] of the Early Cretaceous Gyeongsang Supergroup and acidic volcanic rocks and dykes erupted and intruded in the Late Cretaceous, Miocene intrusive rhyolitic tuffs ($23.1{\pm}0.2Ma{\sim}22.97{\pm}0.13Ma$) and sedimentary rocks of the Yeonghae basin, and the Quaternary sediments. The Triassic Pinkish granites, Jurassic Changpo plutonic rocks and Fine-grained granites are newly defined plutonic rocks in this study. Miocene intrusive rhyolitic tuffs bounded by the Yangsan Fault, which was first discovered in the north of Pohang city, are believed to play an important role in the understanding of the Miocene volcanic activity and the crustal deformation history on the Korean Peninsula. It is confirmed that The NNE-SSW-striking Yangsan Fault penetrating the central part of the study area and branch faults are predominant in the dextral movement and cutting all strata except the Quaternary sediments.

• The Journal of the Petrological Society of Korea
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• v.15 no.4 s.46
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• pp.167-179
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• 2006

Division of granites in the Galmal-Yeonbug area, northern Gyeonggi, can be grey hornblende biotite granite (JHBG), biotite granite (JBG) and pink hornblende biotite granite (CHBG) by lithofacies. JHBG of small stock occurs as medium-grained with grey color and minute sphene. JBG occurs as medium-grained and light grey to grey in the north-east part of the area. The main study target CHBG covers in the north-southeast part of the area, and occurs medium-to coarse-grained with pink color. CHBG shows partly minute miaroles, and pegmatitic pocket with druse texture. From the mineral age data (K-Ar method). JHBG and JBG and CHBG are the igneous activity products of Daebo orogeny with different Jurassic and Bulgugsa disturbance of Cretaceous, respectively. And the age data also agree with geologic occurrences and interpretations of the granites in the field. CHBG consists of quartz, plagioclase, alkali-feldspar, biotite, hornblende, allanite, apatite, zircon, some calcite and opaques. Among them, alkalifeldspar and calcite occur characteristically in mostly perthitic othoclase and secondary filling of minutely miarolitic cavity, respectively. In modal analysis and QAP diagram, CHBG plots in granite field, and especially boundary of monzo-and syeno-granite fields. From the major oxide variations, molar A/CNK, $SiO_{2}\;vs\;K_{2}O$, AMF and so on, CHBG belongs to the acidic, peraluminous and high-K calc-alkaline, and was late differentiation product of single granitic magma. Barium and strontium have also dominantly differentiation trend, and in CaO vs Sr and $K_{2}O$ vs Sr, Sr was more participitated in the fractionation of plagioclase than that of alkali-feldspar. Normalized REE concentrations to chondrite value have parallel and gradual LREE enrichment and HREE depletion patterns, and weak Eu negative anomalies and narrow ranges of normalized Eu can suggest that plagioclase fractionations occurred mildly in the whole CHBG.

• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.83-115
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• 2013

Erroneous fission-track (FT) ages caused by an inappropriate calibration in the initial stage of FT dating were redefined by re-experiments and zeta calibration using duplicate samples. Revised FT zircon ages newly define the formation ages of Yucheon Group rhyolitic-dacitic tuffs as Late Cretaceous to Early Paleocene ($78{\pm}4$ Ma to $65{\pm}2$ Ma) and Gokgangdong rhyolitic tuff as Early Eocene ($52.1{\pm}2.3$ Ma). In case of the Early Miocene volcanics, FT zircon ages from a dacitic tuff of the upper Hyodongri Volcanics ($21.6{\pm}1.4$ Ma) and a dacitic lava of the uppermost Beomgokri Volcanics ($21.3{\pm}2.0$ Ma) define chronostratigraphies of the upper Beomgokri Group, respectively in the southern Eoil Basin and in the Waeup Basin. A FT zircon age ($19.8{\pm}1.6$ Ma) from the Geumori dacitic tuff defines the time of later dacitic eruption in the Janggi Basin. Based on FT zircon ages for dacitic rocks and previous age data (mostly K-Ar whole-rock, partly Ar-Ar) for basaltic-andesitic rocks, reference ages are recommended as guides for stratigraphic correlations of the Miocene volcanics and basements in SE Korea. The times of accumulation of basin-fill sediments are also deduced from ages of related volcanics. Recommended reference ages are well matched to the whole stratigraphic sequences despite complicated basin structures and a relative short time-span. The Beomgokri Group evidently predates the Janggi Group in the Eoil-Waeup basins, while it is placed at an overlapped time-level along with the earlier Janggi Group in the Janggi Basin. Therefore, the two groups cannot be uniformly defined in a sequential order. The Janggi Group of the Janggi Basin can be evidently subdivided by ca. 20 Ma-basis into two parts, i.e., the earlier (23-20 Ma) andesitic-dacitic and later (20-18 Ma) basaltic strata.

• The Journal of the Petrological Society of Korea
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• v.21 no.3
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• pp.335-365
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• 2012

Fission-track (FT) thermochronological records from SE Korean Cretaceous-Paleogene granitic plutons in different fault-bounded blocks reveal contrasting cooling and later thermal histories. Overall cooling patterns are represented by a monotonous (J-shaped) curve in most plutons except some Cretaceous granites retaining a complicated (N-shaped) path due to post-reset re-cooling. Discriminative cooling rates over different temperature ranges can be explained for individual plutons with respect to relative pluton sizes, differences in initial heat loss depending on country rocks, and the presence and proximity of later igneous activity. Even within a single batholith, cooling times for different isotherms were roughly contemporaneous with respect to positions. Insignificant deviations in cooling ages from two different plutons in succession across the Yangsan fault may suggest their contemporaneity before major horizontal fault movement. The extent of later thermal rise recorded locally along the Yangsan and Dongnae fault zones were reached the Apatite Partial Stability Zone ($70-125^{\circ}C$), but did not exceed $200^{\circ}C$. Thermal alteration from fractured zones in the Yangsan-Ulsan fault junction may suggest a thermal reset above $290^{\circ}C$ resulting a complete reset in FT sphene age (31 Ma), caused by a tectonic subsidence in Early Oligocene. A consistency in FT zircon/apatite ages (24 Ma) may imply a sudden rapid cooling over $200-105^{\circ}C$, plausibly related to the abrupt tectonic uplift of the Pohang-Gampo Block including the fault junction in Late Oligocene. A remarkable trend of lower cooling ages for $300-200-100^{\circ}C$ isotherms (i.e., 19% for FT sphene and K-Ar biotite; 20% for FT zircon; 27% for FT apatite) from the east of the Ulsan fault (Pohang-Gampo Block) comparing to the west of the fault may be attributed to retarded cooling times from the Paleogene granites and also reflected by their partially-reduced apatite ages due to later thermal effects.