• Economic and Environmental Geology
• /
• v.3 no.1
• /
• pp.25-34
• /
• 1970

Very few articles are available on geologic structure and genesis of Sangdong scheelite-deposits in spite of the fact that the mine is one of the leading tungsten producer in the world. Sangdong scheelite deposits, embedded in Myobong slate of Cambrian age at the southem limb of the Hambaek syncline which strikes $N70{\sim}80^{\circ}W$ and dips $15{\sim}30^{\circ}$ northeast, comprise six parallel veins in coincide with the bedding plane of Myobong formation, namely four footwall veins, a main vein, and a hangingwall vein. Four footwall veins are discontinuous and diminish both directions in short distance and were worked at near surface in old time. Hangingwall vein is emplaced in brecciated zone in contact plane of Myobong slate and overlying Pungchon limestone bed of Cambrian age and has not been worked until recent. The main vein, presently working, continues more than 1,500 m in both strike and dip sides and has a thickness varying 3.5 to 5 m. Characteristic is the distinct zonal arrangement of the main vein along strike side which gives a clue to the genesis of the deposits. The zones symmetrically arranged in both sides from center are, in order of center to both margins, muscovite-biotite-quartz zone, biotite-hornblende-quartz zone and garnet-diopside zone. The zones grade into each other with no boundary, and minable part of the vein streches in the former two zones extending roughly 1,000 m in strike side and over 1,100 m in dip side to which mining is underway at present. The quartz in both muscovite-biotite-quartz and biotite-hornblende-quartz zones is not network type of later intrusion, but the primary constituent of the special type of rock that forms the main vein. The minable zone has been enriched several times by numerous quartz veins along post-mineral fractures in the vein which carry scheelite, molybdenite, bismuthinite, fluorite and other sulfide minerals. These quartz veins varying from few centimeter to few tens of centimeter in width are roughly parallel to the main vein although few of them are diagonal, and distributed in rich zones not beyond the vein into both walls and garnet-diopside zone. Ore grade ranges from 1.5~2.5% $WO_3$ in center zone to less than 0.5% in garnet-diopside zone at margin, biotite-hornblende-quartz zone being inbetween in garde. The grade is, in general, proportional to the content of primary quartz. Judging from regional structure in mid-central parts of South Korea, Hambaek syncline was formed by the disturbance at the end of Triassic period with which bedding thrust and accompanied feather cracks in footwall side were created in Myobong slate and brecciated zone in contact plane between Myobong slate and Pungchon limestone. These fractures acted as a pathway of hot solution from interior which was in turn differentiated in situ to form deposit of the main vein with zonal arrangement. The footwall veins were developed along feather cracks accompanied with the main thrust by intrusion of biotite-hornblende-quartz vein and the hangingwall vein in shear zone along contact plane by replacement. The main vein thus formed was enriched at later stage by hydrothermal solutions now represented by quartz veins. The main mineralization and subsequent hydrothermal enrichments had probably taken place in post-Triassic to pre-Cretaceous periods. The veins were slightly displaced by post-mineral faults which cross diagonally the vein. This hypothesis differs from those done by previous workers who postulated that the deposits were formed by pyrometasomatic to contact replacement of the intercalated thin limestone bed in Myobong slate at the end of Cretaceous period.

• The Journal of the Petrological Society of Korea
• /
• v.25 no.3
• /
• pp.211-230
• /
• 2016

Detailed mapping along the Keumwang fault reveals a complex history of multiple brittle reactivations following late Jurassic and early Cretaceous ductile shearing. The fault core consists of a 10~50 m thick fault gouge layer bounded by a 30~100 m thick damaged zone. The Pre-cambrian gneiss and Jurassic granite underwent at least six distinct stages of fault movements based on deformation environment, time and mechanism. Each stage characterized by fault kinematics and dynamics at different deformation environment. Stage 1 generated mylonite series along the Keumwang shear zone by sinistral ductile shearing during late Jurassic and early Cretaceous. Stage 2 was a mostly brittle event generating cataclasite series superimposed on the mylonite series of the Keumwang shear zone. The roundness of pophyroclastes and the amount of matrix increase from host rocks to ultracataclasite indicating stronger cataclastic flow toward the fault core. At stage 3, fault gouge layer superimposed on the cataclasite generated during stage 2 and the sedimentary basins (Umsung and Pungam) formed along the fault by sinistral strike-slip movement. Fragments of older cataclasite suspended in the fault gouge suggest extensive reworking of fault rocks at brittle deformation environments. At stage 4, systematic en-echelon folds, joints and faults were formed in the sedimentary basins by sinistral strike-slip reactivation of the Keumwang fault. Most of the shearing is accommodated by slip along foliations and on discrete shear surfaces, while shear deformation tends to be relatively uniformly distributed within the fault damage zone developed in the mudrocks in the sedimentary basins. Fine-grained andesitic rocks intruded during stage 4. Stage 5 dextral strike-slip activity produced shear planes and bands in the andesitic rocks. ESR(Electron Spin Resonance) dates of fault gouge show temporal clustering within active period and migrating along the strike of the Keumwang fault during the stage 6 at the Quaternary period.

• The Korean Journal of Petroleum Geology
• /
• v.8 no.1_2 s.9
• /
• pp.1-43
• /
• 2000

A comparison study for understanding a stratigraphic response to tectonic evolution of sedimentary basins in the Yellow Sea and adjacent areas was carried out by using an integrated stratigraphic technology. As an interim result, we propose a stratigraphic framework that allows temporal and spatial correlation of the sedimentary successions in the basins. This stratigraphic framework will use as a new stratigraphic paradigm for hydrocarbon exploration in the Yellow Sea and adjacent areas. Integrated stratigraphic analysis in conjunction with sequence-keyed biostratigraphy allows us to define nine stratigraphic units in the basins: Cambro-Ordovician, Carboniferous-Triassic, early to middle Jurassic, late Jurassic-early Cretaceous, late Cretaceous, Paleocene-Eocene, Oligocene, early Miocene, and middle Miocene-Pliocene. They are tectono-stratigraphic units that provide time-sliced information on basin-forming tectonics, sedimentation, and basin-modifying tectonics of sedimentary basins in the Yellow Sea and adjacent area. In the Paleozoic, the South Yellow Sea basin was initiated as a marginal sag basin in the northern margin of the South China Block. Siliciclastic and carbonate sediments were deposited in the basin, showing cyclic fashions due to relative sea-level fluctuations. During the Devonian, however, the basin was once uplifted and deformed due to the Caledonian Orogeny, which resulted in an unconformity between the Cambro-Ordovician and the Carboniferous-Triassic units. The second orogenic event, Indosinian Orogeny, occurred in the late Permian-late Triassic, when the North China block began to collide with the South China block. Collision of the North and South China blocks produced the Qinling-Dabie-Sulu-Imjin foldbelts and led to the uplift and deformation of the Paleozoic strata. Subsequent rapid subsidence of the foreland parallel to the foldbelts formed the Bohai and the West Korean Bay basins where infilled with the early to middle Jurassic molasse sediments. Also Piggyback basins locally developed along the thrust. The later intensive Yanshanian (first) Orogeny modified these foreland and Piggyback basins in the late Jurassic. The South Yellow Sea basin, however, was likely to be a continental interior sag basin during the early to middle Jurassic. The early to middle Jurassic unit in the South Yellow Sea basin is characterized by fluvial to lacustrine sandstone and shale with a thick basal quartz conglomerate that contains well-sorted and well-rounded gravels. Meanwhile, the Tan-Lu fault system underwent a sinistrai strike-slip wrench movement in the late Triassic and continued into the Jurassic and Cretaceous until the early Tertiary. In the late Jurassic, development of second- or third-order wrench faults along the Tan-Lu fault system probably initiated a series of small-scale strike-slip extensional basins. Continued sinistral movement of the Tan-Lu fault until the late Eocene caused a megashear in the South Yellow Sea basin, forming a large-scale pull-apart basin. However, the Bohai basin was uplifted and severely modified during this period. h pronounced Yanshanian Orogeny (second and third) was marked by the unconformity between the early Cretaceous and late Eocene in the Bohai basin. In the late Eocene, the Indian Plate began to collide with the Eurasian Plate, forming a megasuture zone. This orogenic event, namely the Himalayan Orogeny, was probably responsible for the change of motion of the Tan-Lu fault system from left-lateral to right-lateral. The right-lateral strike-slip movement of the Tan-Lu fault caused the tectonic inversion of the South Yellow Sea basin and the pull-apart opening of the Bohai basin. Thus, the Oligocene was the main period of sedimentation in the Bohai basin as well as severe tectonic modification of the South Yellow Sea basin. After the Oligocene, the Yellow Sea and Bohai basins have maintained thermal subsidence up to the present with short periods of marine transgressions extending into the land part of the present basins.

• Journal of the Korean earth science society
• /
• v.34 no.3
• /
• pp.235-248
• /
• 2013

The purpose of this study is to investigate a feasibility of a small mountain as a field work site on geological features in Earth sciences classes at all levels. Mt. Geumdang with the height of 305 meters from the sea level is located in the metropolitan city of Gwangju, southern part of Korea. The study reviews the human and natural geography, geological features, geomorphic resources, landscapes, and conveniences of the mountain for a possibility of meaningful field work. The population within the distance of 5 km from the mountain stands at about 620,000 and 170,000 of them are students and teachers. Mt. Geumdang has a warm temperature climate with low rainfall throughout the year, so it seems suitable for a field survey. Road network and public transportation system around the area are well-developed and easily accessible. Mt. Geumdang shows various rock type and geological structures. The basement rock is Gwangju granite, which is plutonic body of the Jurassic period. Also, granophyre (micrographic granite) and various volcanic rocks distributed as bedded tuff, lapilli tuff, and rhyolite of the Cretaceous period. Many andesitic and felsic dykes were intruded into the rock by joint system. In Mt. Geumdang, many geomorphic resources are found such as U shaped mountain, joint, fault, lamination, gnamma, tor, cliff, groove, block stream and block field, regolith, and saprolite. It has a beautiful mountain scenery including the view of whole shape of Mt. Mudeung, panoramic view of the town, Pungam lake, World Cup stadium and sunrise and sunset. Furthermore, the area has ecologic study facilities related to geology, emergency medical and convenience facilities for field works. In conclusion, Mt. Geumdang is highly feasible for geological field studies at all levels.

• Journal of the Korean earth science society
• /
• v.26 no.5
• /
• pp.443-458
• /
• 2005

Late Quaternary deposits of the core in the western area of the Nakdong River delta consist of four sedimentary units: Unit I, II, III and IV, in ascending order, controlled by the sea-level change since the last interglacial period. Unit I unconformable overlying Cretaceous basement rocks is composed of sandy gravel and sand deposited in a fluvial channel before the first marine transgression. Unit II composed of stiff massive mud is interpreted as a shallow marine deposits formed during the last interglacial period (probably MIS 5). The development of the fissures coated with oxidized materials in the upper part of Unit II is a feature of subaerial exposure, which indicates erosional contact with the upper Unit III. Unit III is made up of soft massive mud and soft shelly massive mud deposited in a tidal flat and a inner shelf, respectively, since the Holocene transgression (about 9,000 yr BP). Unit Ⅳ consisted of soft shell bedded mud and yellowish sandy mud was deposited in the delta environments during the regression (after about 5,000 yr BP). The lower shell bedded mud was deposited in a tidal flat and the upper sandy mud was deposited in the floodplain corresponding to present site of the Nakdong River delta.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2008.10a
• /
• pp.85-92
• /
• 2008

National Oceanographic Research Institute is carrying out an oceanographic survey for the entire sea areas around Korean Peninsula annually starting with the East Sea from 1996 by establishing a national oceanographic basic map survey plan for the sea areas under the jurisdiction of Korea, so this paper used the oceanographic geomagnetism data measured at the southern area of the Yellow Sea using 'Hae Yang 2000' in 1999, aiming at clarifying the cause of geomagnetic abnormality zone during the course of treating and analyzing the geomagnetic data. For treatment of magnetic data, we obtained electromagnetic force values and geomagnetic abnormality values around the investigated sea area through a process of searching and removal of bad data, correction of sensor positions, correction of magnetic field effects around the hull, correction of diurnal variation, normal correction, correction of cross point errors, etc. The electromagnetic force distribution around the investigated sea area was $49000\;{\sim}\;51600\;nT$, which is judged to be within the normal electromagnetic force intensity distribution range around the Yellow Sea. The isodynamic lines are distributed in Northeast-Southwest direction, and electromagnetic force values are increasing toward the northwest. The result of comparing the magnetic abnormality around the sea area among $124^{\circ}$ 49' 48" E, $35^{\circ}$ 10' 48" N $\sim$ $125^{\circ}$ 7' 48" E, and $35^{\circ}$ 33' 00" N sections with the elastic wave cross section and the result of modeling coincide well with the underground geological structure clarified from the existing elastic wave survey cross section. Therefore, it is judged that the distribution of magnetic force abnormality generally shows the effect pursuant to the distribution of the sedimentary basins in the Tertiary period and the bedrocks in the Cretaceous period which are well developed in the bottom of the sea.

• Journal of Korean Society of Forest Science
• /
• v.108 no.2
• /
• pp.216-223
• /
• 2019

This study was conducted to measure the changes in the geological and soil properties following slow-moving landslide events in Yangbuk-myun and Gyungju-si, Gyeongsangbuk-do, South Korea. The geological characteristics of the study site comprised black shale in the Gyeongsang nodal group formed in the Cretaceous period and quartz feldspar carcinoma in the east side with conglomerate in the Yeonil group formed in the Quaternary period. The study site exhibited the geologic characteristics of a slow-moving landslide with severely weathered rocks. The maximum collapsing depth of the slow-moving landslide was 12.0 m with colluvial deposits. The strike and joint aspects in the slope areas of the slow-moving landslides were $N46^{\circ}E$ in lower slope and $N62^{\circ}E$ in upper slope, respectively. Soil hardness of ${\leq}20cm$ deep was not measured because of the completely disturbed soil resulting from soil creeping. Soil from 25 to 90 cm deep was 1.4-4.7 times softer in the slow-moving landslide areas than in the undisturbed or natural forests. Soil bulk density was $1.24-1.29g/cm^3$ in land creep areas. Soil bulk in both areas was 1.6 times denser than that in the natural forest. The soil pore space was 51.5-53.3% in the land creep areas. The values are 1.3-1.4 times lower than those within the natural forest. Black shale areas showed the lowest coefficient of permeability (8.75 E-06 cm/s) and mesopore ratio (pF 2.7: 9.8%) compared with those resulting from other study areas.

• Economic and Environmental Geology
• /
• v.28 no.4
• /
• pp.337-350
• /
• 1995

The Hwacheon-ri mineralized area is located within the Cretaceous Gyeongsang Basin of the Korean peninsula. The mineralized area includes the Hwacheon, Daeweon, Kuryong and Cheongryong mines. Each of these mines occurs along copper-bearing hydrothermal quartz veins that crosscut late Cretaceous volcanic rocks, although some disseminated ores in host rocks also exist locally. Mineralization can be separated into three distinct stages (I, II, and III) which developed along preexisting fracture zones. Stage I is ore-bearing, whereas stages II and III are barren. The main phase of ore mineralization, stage I, can be classified into three substages (Ia, Ib and Ic) based on ore mineral assemblages and textures. Substage Ia is characterized by pyrite-arsenopyrite-molybdenite-pyrrhotite assemblage and is most common at the Hwacheon deposit. Substage Ib is represented by main precipitation of Cu, Zn, and Pb minerals. Substage Ic is characteristic of hematite occurrence and is shown only at the Kuryong and Cheongryong deposits. Some differences in the ore mineralization at each mine in the area suggest that the evolution of hydrothermal fluids in the area varied in space (both vertically and horizontally) with respect to igneous rocks relating the ore mineralization. Fluid inclusion data show that stage I ore mineralization mainly occurred at temperatures between ${\approx}350^{\circ}$ and ${\approx}200^{\circ}C$ from fluids with salinities between 9.2 and 0.5 wt.% eq. NaCl. In the waning period of substage Ia, the high temperature and salinity fluid gave way to progressively cooler, more dilute fluids of later substage Ib and Ic (down to $200^{\circ}C$, 0 wt.% NaCl). There is a systematic decrease in the calculated ${\delta}^{18}O_{H2O}$ values with paragenetic time in the Hwacheon-ri hydrothermal system from values of ${\approx}2.7$‰ for substage Ia, through ${\approx}-2.8$‰ for substage Ib, to ${\approx}-9.9$‰ for substage Ic. The ${\delta}D$ values of fluid inclusion water also decrease with decreasing temperature (except for the Daeweon deposit) from -62‰ (substage Ia) to -80‰ (substage Ic and stage III). These trends are interpreted to indicate the progressive cooler, more oxidizing unexchanged meteoric water inundation of an initial hydrothermal system which is composed of highly exchanged meteoric water. Equilibrium thermodynamic interpretation of the mineral assemblages with the variation in amounts of chalcopyrite through the paragenetic time, and the evolution of the Hwacheon-ri hydrothermal fluids indicate that the solubility of copper chloride complexes in the hydrothermal system was mainly controlled by the variation of temperature and $fo_2$ conditions.

• Journal of the Korean earth science society
• /
• v.25 no.6
• /
• pp.484-494
• /
• 2004

The Soowang Au-Ag deposits occur as quartz veins which filled fissures in middle Cretaceous porphyritic granite an/or gneiss of the Precambrian Sobaegsan gneiss complex. The paragenetic studies suggest that vein filling can be divided into four identifiable stages (I to IV). Stage I is the main sulfide stage, characterized by the deposition of base-metal sulfide and minor electrum. Stage II is the electrum stage, whereas stage III represents a period of the deposition of silver-bearing sulfosalts and minor electrum. Stage IV is the post ore stage. Mineralogical and fluid inclusion evidences suggest that mineralization of the Soowang deposits were deposited by the cooling of the fluids from initial high temperatures 300$^{\circ}C$ to later low temperatures 150$^{\circ}C$. The salinity of the fluids were moderate, ranging from 10.4wt.% equivalent NaCl in sphalerite to 3.1wt.% equivalent NaCl in barite. The gold-silver mineralization of the Soowang mine occurred at temperatures between 140 and 250$^{\circ}C$ from fluids with log $fs_2$ from -12 to -18 atm. A consideration of the pressure regime during ore deposition, based on the fluid inclusion evidence of boiling, suggests lithostatic pressure of less than 210 bars. This pressure condition indicates that vein system of the Soowang deposit formed at depth around 800 m below the surface at the time of gold-silver mineralization.

• Economic and Environmental Geology
• /
• v.30 no.2
• /
• pp.81-87
• /
• 1997

Chonnam and Kyongsang clay alteration areas are distributed in volcanic fields of the Yuchon Group in late Cretaceous period. The host rock of the Chonnam alteration area is generally acidic and that of the Kyongsang alteration area is acidic to dominantly intermediate volcanics. The important difference of two alteration areas is source of fluid; the Chonnam alteration area is characterized by dominantly meteoric water and the Kyongsang alteration area is characterized by dominantly magmatic water. Accordingly, the high temperature minerals such as pyrophyllite and andalusite, and boron bearing minerals such as dumortierite and tourmaline are common in the Kyongsang alteration area. In contrast to this, the lower temperature minerals such as kaolin and alunite are common in the Chonnam alteration area. The mineralogical difference of two alteration areas were depended on the difference of the formation temperature of clay deposits. The other important geochemical difference is the chemistry of hydrothermal solution such as pH. The alteration of "acid-sulfate type" with alteration mineral assemblage of alunite-kaolin-quartz is dominant in the Chonnam alteration area, which was caused by the attack of strong acid and acid solution. In contrast to this, the that of "quartz-sericite type" with the mineral assemblage of sericite-quartz is dominant in the Kyongsang alteration area, which was caused by the attack of neutral or weak acid solution. Also, the Kyongsang and Chonnam alteration areas show the difference in structural setting; the Chonnam alteration area is commonly associated with silicic domes and the Kyongsang alteration area is commonly associated with calderas.