• Journal of the Geological Society of Korea
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• v.54 no.5
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• pp.513-527
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• 2018

We have carried out granulometry and component analysis on pyroclastic deposits of the Maljandeung Tuff, Ulleung Island, to interpret the eruption types and prime dynamic mechanisms. It is divided into three members in the extracaldera area, each of which comprises the lithofacies of coarse tuffs and lapillistones in the lower part, and pumice deposits in upper one. The lithofacies present quantitative evidences in the granularity and component distribution patterns. As compared to the pumice deposits, the coarse tuffs and lapillistones exhibit a relative increase in both the lithic/juvenile and the crystal/juvenile ratios, and a preferential fragmentation of the juvenile fraction. The abundance of lithics and crystals in the tuffs and lapillistones can be attributed to preferential fragmentation of the aquifer-hosting rocks due to explosive evaporation of ground water, and indirect enrichment in lithics and crystals due to removal of juvenile fines from eruptive cloud. The above data exhibit that early phreatopmagmatic phase was followed by purely magmatic fragmentation phases. The coarse tuffs and lapillistones suggest phreatoplinian eruption derived from explosive interaction of magma with ground water near the conduit, while pumice deposits indicate magmatic eruption by magmatic explosion from juvenile gas pressure. In early stage, phreatoplinian eruption occurred from explosive magma/water interaction in connecting confining water with drawdown of the magma column in the conduit; Later it shifted to plinian eruption by explosive expansion of only magmatic volatiles in intercepting water influx due to higher magmatic gas pressure than confining water pressure with rising of the magma column in the conduit.

• Economic and Environmental Geology
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• v.55 no.5
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• pp.465-475
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• 2022

The seafloor massive sulfide deposits are important mineral resources for base and precious metals, and their ore genesis and metal contents are mainly controlled by wall-rock leaching process and/or magmatic volatile input from the underlying magma chamber. However, the contribution of two different metal sources to the seafloor hydrothermal mineralization significantly varies in diverse geological settings and thus still remains controversial. In this review, mineralogical and geochemical characteristics of SMS deposits from mid-ocean ridges (MORs) and volcanic arcs were investigated to understand the contribution from different metal sources and to suggest future challenges that need to be addressed. As a result, the genetic occurrences of enargite and cubanite, galena and barite indicate the effects of magmatic input and water-rock interaction, respectively. Also, the distributional behaviors of Co, As, and Hg in pyrite and FeS content of sphalerite could be useful empirical indicators to discriminate the significant roles of different metal sources between MOR and Arc settings. To date, as most studies have focused on sulfide samples recovered from the seabed, further studies on magmatic sulfides and sulfate minerals are required to fully understand the genetic history of SMS deposits.

• The Korean Journal of Quaternary Research
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• v.23 no.1
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• pp.38-41
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• 2009

Results from the most recent decade of Mars' missions to Mars highlight a liquid water and water-ice sculpted landscape. Evidence includes layered sedimentary sequences with weathered outcrops, debris flows, fluvial valleys, alluvial fans, deltas, glacial and periglacial landscapes, and geochemical/mineralogical signatures of aqueous activity, including the formation of sulfates and clays, and the leaching and deposition of elements such as potassium, thorium,and iron. Such evidence indicates weathered zones and possible paleosols in stratigraphic sequences, transport of water and rock materials to sedimentary basins, and the possible formation of extensive transient lakes and possibly transient oceans on Mars. This new evidence is consistent with Viking-era geologic investigations that reported magmatic-driven flooding, ponding to form large water bodies in the northern plains, and transient (tens of thousand of years) hydrological cycles. It may even indicate aqueous activity at present. Both endogenic (magmatic driven) and exogenic (both impact cratering and changes in orbital parameters) have influenced paleohydrologic and environmental change on Mars. Abundance of water and dynamic activity would be decisively important for the possibility of past and present life on Mars.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.519-529
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• 1997

Volcanic rocks including rhyolitic tuff, rhyolite and welded tuff in the Bupyeong silver mine area form a topographic circular structure which is interpreted as a resurgent caldera. Granitic rocks are emplaced inside and outside area of the circular structure. Pervasive silver mineralization took place in the rhyolitic rock of the southwestern margin of the caldera. Gas and fluid incluson studies were carried out to investigate the petrogenetic evolution and post-magmatic alteration for the rhyolitic and granitic rocks. Gas compositions are characterized by a low $CH_4/CO_2$ ratio (0.004-0.005) for rhyolitic and inside granitic rocks and a high $CH_4/CO_2$ ratio (0.01~0.29) for outside granitic rocks such as the Kimpo and Incheon granites. Homogenization temperature of solid daughter mineral bearing fluid inclusion (III and IV types) and two phase fluid inclusion (I and II types) for quartz in the Bupyeong granites range from 400 to $500^{\circ}C$ and 121 to $514^{\circ}C$, respectively. Salinties vary from 20 to 30 wt% NaCl for type III and IV inclusions and less than 20 wt % NaCl for type I and II inclusions. The fluid inclusion data shows a considerable influx of the meteoric water toward post magmatic alteration stage.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.20-23
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• 2003

Low-sulfidation style ore deposits, the major source of Au, Ag, and Hg, are formed from neutral-pH, reduced hydrothermal solutions close to equilibrium with their host rocks. The waters are low-salinity (〈1 wt % NaCl equiv.) but relatively gas rich (1-2 wt % $CO_2$), and are largely meteoric water. However, the contribution of magmatic components to the epithermal system, its temporal importance, and its relation to the source of ore metals are largely controversial. (omitted)

• Economic and Environmental Geology
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• v.25 no.1
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• pp.41-50
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• 1992

Mineral assemblages, mineral chemistries and stable isotope compositions of altered rocks of the Ogmae, Seongsan, Haenam and Gusi mines near the Haenam volcanic field in the southwestern part of the Korea peninsula were studied. Characteristic hydrothermal alteration zones in these deposits occurring in the Cretaceous volcanics and volcanogenic sediments, acidic tuff, and rhyolite, were outlined. Genetic environment with particular reference to the spatial and temporal relationships for these deposits were considered. The alteration zones defined by a mineral assemblage in the Ogmae and Seongsan deposits can be classified as alunite, pyrophyllite, kaolinite or dickite, quartz, illite or illite/smectite. Alunite was not developed in the Gusi and Haenam deposits. Boundaries between the adjacent zones are always gradational except for vein-type alunite. Alteration zones are superimposed upon each other in some localities. These deposits formed $71.8{\pm}2.8{\sim}76.6{\pm}2.9$ Ma ago, which is the almost same age of later volcanic rocks $79.4{\pm}1.7{\sim}82.8{\pm}1.2$ Ma, the Haenam Group, corresponding to Campanian. It indicates that hydrothermal alteration of these deposits appeared to be related to felsic volcanism in the area. Consideration of the stability between kaolinite, alunite, pyrite and pyrophyllite, and the geothermometry based on the mineral chemistry of illite and chlorite suggests that the maximum formation temperature for alunite and pyrophyllite can be estimated at about $250^{\circ}C$ and $240{\sim}290^{\circ}C$, respectively. It also suggests that these deposits were formed by acidic sulfate solution with high aqueous silica and potassium activity in a shallow depth environment. Compositional variation of alunite also suggests that the physico-chemical conditions fluctulated considerably during alteration processes, indicating shallow depth environment. The Haenam deposit was formed at a relatively greater depth than the others. The sulfur isotope composition of alunite and pyrite indicates that sulfur probably had a magmatic source, and the oxygen isotope composition for kaolinite indicates that the magmatic hydrothermal solution was diluted by circulating meteoric water.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.1-14
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• 1998

Dangsanbong volcano, which is located on the coast of the western promontory of Cheju Island, occurs in such a regular pattern on the sequences which represent an excellent example of an eruptive cycle. The volcano comprises a horseshoe-shaped tuff cone and a younger nested cinder cone on the crater floor, which are overlain by a lava cap at the top of the cinder cone, and wide lava plateau in the moat between two cones and in the northern part. The volcanic sequences suggest volcanic processes that start with Surtseyan eruption, progress through Strombolian eruption and end with Hawaiian eruption, and then are followed by rock fall from sea cliff of the tuff cone and by air fall from another crater. It is thought that the eruptive environments of the tuff cone could be mainly emergent because the present cone is located on the coast, and standing body of sea water could play a great role. It is thought that the now emergent part of the tuff cone was costructed subaerially because there is no evidence of marine reworking. The emergent tuff cone is characterized by distinctive steam-explosivity that results primarily from a bulk interaction between rapidly ascending magma and external water. The sea water gets into the vent by flooding accross or through the top or breach of northern tephra cone. Dangsanbong tuff cone was constructed from Surtseyan eruption which went into with tephra finger jetting explosion in the early stage, late interspersed with continuous upruch activities, and from ultra-Surtseyan jetting explosions producting base surges in the last. When the enclosure of the vent by a long-lived tephra barrier would prevent the flooding and thus allow the vent to dry out, the phreatomagmatic activities ceased to transmit into magmatic activity of Strombolian eruption, which constructed a cinder cone on the crater floor of the tuff cone Strombolian eruption ceased when magma in the conduit gradually became depleted in gas. In the Dangsanbong volcano, the last magmatic activity was Hawaiian eruption which went into with foundation and effusion of basalt lava.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.178-179
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• 2003

Mesothermal, tellurium-bearing gold-silver vein mineralization of the Yuryang mine was formed in mineralogically complex quartz-sulfide veins that filled the fault fractures in Precambrian gneiss within Gyeonggi Massif. Ore grades average 179 g/ton gold with a gold/silver ratio of 1.5 : 1. Ore mineralization was deposited in single stage. Major ore mineralization can be divided into two mineralization phases with increasing paragenetic time: Fe-sulfide and base-metal mineralization phase $\rightarrow$ telluride mineralization phase. (omitted)

• Economic and Environmental Geology
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• v.26 no.3
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• pp.267-278
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• 1993

Serpentinite rocks which are composed mainly of olivine, serpentine and clinopyroxene, cropped out in the anorogenic Kyongsang sedimentary basin of South Korea. The serpentinites contain high content of MgO (36.87~41.99%) and 47~67 ppm Co, 1185~2042 ppm Ni and 979~3582 ppm Cr, which are quite similar to those of ultrabasic rocks such as peridotite and dunite. Isotopic compositions of serpentinites range from -95.5 to -105.7‰ in ${\delta}D$ and +1.7 to 7.1‰ in ${\delta}^{18}O$ corresponding to the continental antigorite type. A wide variation of oxygen isotopic values and $H_2O^+$ content of serpentinites reflect the different water/rock ratios during serpentinization processes. Formation temperature of serpentine minerals are estimated to be unusually high temperature of $488{\sim}646^{\circ}C$ by serpentine-magnetite isotopic fractionation, which belong to continental antigorite type. Calculated ${\delta}^{18}O$ value of serpentinized fluid during serpentinization is suggested that the hydrothermal fluid responsible for serpentinization be originated from the magmatic fluid with a minor influx of paleo-meteoric water in this area.

• Economic and Environmental Geology
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• v.29 no.2
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• pp.159-170
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• 1996

The gold-silver deposits of the Nakcheon, Eunchi and Jungbong mine in the northern Taebagsan mining district are composed of fissure fil1ing veins emplaced in Precambrian meta-sediments and Jungbongsan granite. Based on the changes of ore texture and mineralogy, ore mineral chemistry, fluid inclusion and mineralizing condition, a regional zoning is recognized from the Nakcheon to the Eunchi and Jungbong ore deposits, and this trend of zoning is also recognized by stable isotope compositions. Stable isotope compositions show that the source of su1fur and carbon is mainly igneous origin, and the water of ore fluid in the Nakcheon ore deposits is mainly magmatic origin but much of meteoric water is involved in ore fluid of the Eunchi and Jungbong ore deposits. The ore deposits of study area is polymetallic meso to epithermal type genetically related to the acidic igneous pluton. Due to the differntial erosion level and mineralized depth, each ore deposits has a slightly different characteristic of mineralization; The Nakcheon ore deposits belong to meso-epithermal type, but the Eunchi and Jungbong ore deposits belong to epithermal type.