• Economic and Environmental Geology
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• v.23 no.2
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• pp.135-141
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• 1990

A number of alunite and pyrophyllite deposits occur around the Haenam area where Cretaceous volcanic and volcanogenic sediments are widely distributed. The K-Ar ages of alunite, sericite and whole rocks collected from alunite and pyrophyllite deposits and unaltered rocks representing various stratigraphic horizon of the area were determined and their formation stage was discussed. The ages of volcanic rocks range between $68.6{\pm}1.9$ and $94.1{\pm}2.0$ Ma corresponding to Cenomanian-Maastrichtian of upper Cretaceous. Andesitic rock gives $94.1{\pm}2.0$. Rhyolite and acidic tuffs give $79.47{\pm}1.7$ and $82.8{\pm}1.2$ Ma corresponding to Campanian. The later stage andesite gives $68.6{\pm}1.9$ Ma of Maastrichtian. The results suggest that volcanism of the area can be devided into three different stages. The ages of alunite and sericite range $71.8{\pm}2.8$ to $76.6{\pm}2.9$ Ma of late Campanian to early Maastrichtian which is rather earlier than the age of granite(67 Ma). It indicates that the alteration ages of these clay mineral deposits appeared to be related with its volcanism rather than the hydrothermal stage of granite of this area.

• Economic and Environmental Geology
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• v.29 no.5
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• pp.561-573
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• 1996

The igneous rocks in the Goseong area, the southwestern part of the Gyeongsang basin, are composed of the volcanic rocks, Bulgugsa granites and intrusive andesites. The volcanic rocks are andesitic lapilli tuff, dacite and rhyolite. The granites are mainly of hornblende-biotite granite and intruded into the sedimentary basement and the volcanic rocks. The intrusion of andesitic dyke is thought to be the latest igneous activity in the area. In the variation diagrams of the major oxides, the three igneous rock types show different variational trends, indicating that they were from the different magmatic pulses. K-Ar radiometric ages suggest that the igneous activity in the Goseong area had occurred during late Cretaceous period. The ages of the volcanic rocks seem likely to have become younger due to the thermal effect by the granitic intrusion. The major element compositoinal variation of the granites from the Goseong area are compared with those from the Jindong, Geoje and Masan areas. By the comparison, it is easily understood that the Jindong granites are fairly different from the other three granites. On the other hand, the Goseong, Geoje and Masan granites generally show similar variational trends with each other, suggesting that they are of similar genetic origin. Combining the similarity of the geochemical features and the difference of the intruding ages between the Goseong and Masan granites, it seems like that the magma generation from the same source materials had occurred at a temporal interval.

• Economic and Environmental Geology
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• v.32 no.3
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• pp.227-236
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• 1999

The Daeyou pegmatite is located at the central westerm part of the peninsula. Geology of the mine area consists mainy of pre-Combrian granite gneiss and leucoratic gneiss which are intruded by Mesozoic granites. The pegmatite deposits occur within granite gneiss. Most of pegmatites contain quartz, perthite, microcline-perthite, microcline, sodic plagioclase and tourmaline as dominant minerals with accessory minerals of mica (muscovite, biotite, sericite)and pyrite. Tourmaline occurs as four types: 1) unaltered single crystals, 2) patially sericitized grains bordered by sericite assemblage, 3) tourmaline intergrown with feldspar and qurtz grains, and 4) tourmaline introduced veinlet/ On the basic of optical, X-ray diffraction and chemical analysis, the composition of tourmaline mostly falls on the schorl-elbaite join, in the composition of tourmaline mostly falls on the schorl-elbraite join, in the composition of schorl end member from 0 to about 50%. In spite of the different occurrences, chemical composition of tourmaline shows the limited ranges as follows: $SiO_{2}$ (34.53~35.01 wt.%), $Al_{2}O_{3}$ (33.58~34.26wt.%), FeO (13.73~14.17wt.%), $Na_{2}O$ (1.60~1.72wt.%), MgO (0.56~0.72wt.%), MnO (0.12~0.18wt.%), CaO (0.02~0.06wt.%), $K_{2}O$(0.02~0.03wt.%) $TiO_{2}$ (0.02~0.05wt.%) and $Cr_{2}O_{3}$ (0.02~0.03wt.%). K-Ar ages of the muscovite and sericite fall between 1010$\pm$15 and 1074$\pm$16Ma and between 161.56$\pm$3.09 and 161.67$\pm$Ma, respectivrly. This means that hydrothrmal alteration occurred during middle Jurassic, whereas the pegmatite was initally formed during the late proterozoic age.

• The Journal of the Petrological Society of Korea
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• v.16 no.2 s.48
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• pp.82-99
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• 2007

The Paleogene dikes intruding into the late Cretaceous granodiorite are pervasively observed in the Irun-myeon, eastern Geoje Island. They are classified into three groups: NW-trending acidic dike swarm and WNW- (A-Group) and $NS{\sim}NNE-trending$ (B-Group) basic dike swarms. Based on their cross-cutting relationships, the earliest is the acidic dike group and fellowed by A- and B-Groups in succession. The acidic dikes seem to have intruded into tension gashes induced by the sinistral strike-slip faulting of the Yangsan fault system during the late $Cretaceous{\sim}early$ Paleogene. In terms of rock-type, orientation, age, and geochemistry, A-Group and B-Group are intimately correlated with the intermediate and basic dike swarms in the Gyeongju-Gampo area, respectively. These results significantly suggest that the corresponding dike swarms are genetically related. Based on the K-Ar and Ar-Ar age data, A- and B- Groups were intruded during $64{\sim}52\;Ma$ and $51{\sim}44\;Ma$, respectively. The result means that the direction of tensional stress in and around the SE Korean peninsula was changed abruptly from NNE-SSW to $EW{\sim}WNW-ESE$ at about 51 Ma. Considering the tectonic environments during the Paleogene, it is interpreted that A-Group was injected along the WNW-trending tensional fractures developed under an regional sinistral simple shear regime which was caused by the north-northwestward oblique subduction of the Pacific plate beneath the Eurasian plate. Meanwhile, the regional stress caused by the collision of India and Eurasia continents at about 55 Ma was likely propagated to the East Asia at about 51 Ma, and then the East Asia including the Korean peninsula was extruded eastwards as a trench-rollback and the dip of downgoing slab of the Pacific plate was abruptly steepened. As a result, the strong suction-force along the plate boundary produced a tensional stress field trending EW or WNW-ESE in and around the Korean peninsula, which resultantly induced B-Group to intrude passively into the study area.

• Economic and Environmental Geology
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• v.47 no.4
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• pp.317-333
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• 2014

The Pocheon iron (-copper) deposit, located at the northwestern part of the Precambrian Gyeonggi massif in South Korea, genetically remains controversial. Previous researchers advocated a metamorphosed (-exhalative) sedimentary origin for iron enrichment. In this study, we present strong evidences for skarnification and Fe mineralization, spatially associated with the Myeongseongsan granite. The Pocheon deposit is composed of diverse carbonate rocks such as dolostone and limestone which are partially overprinted by various hydrothermal skarns such as sodic-calcic, calcic and magnesian skarn. Iron (-copper) mineralization occurs mainly in the sodic-calcic skarn zone, locally superimposed by copper mineralization during retrograde stage of skarn. Age data determined on phlogopites from retrograde skarn stage by Ar-Ar and K-Ar methods range from $110.3{\pm}1.0Ma$ to $108.3{\pm}2.8Ma$, showing that skarn iron mineralization in the Pocheon is closely related to the shallow-depth Myeongseongsan granite (ca. 112 Ma). Carbon-oxygen isotopic depletions of carbonates in marbles, diverse skarns, and veins can be explained by decarbonation and interaction with an infiltrating hydrothermal fluids in open system ($XCO_2=0.1$). The results of sulfur isotope analyses indicate that both of sulfide (chalcopyrite-pyrite composite) and anhydrites in skarn have very high sulfur isotope values, suggesting the $^{34}S$ enrichment of the Pocheon sulfide and sulfate sulfur was derived from sulfate in the carbonate protolith. Shear zones with fractures in the Pocheon area channeled the saline, high $fO_2$ hydrothermal fluids, resulting in locally developed intense skarn alteration at temperature range of about $500^{\circ}$ to $400^{\circ}C$.

• Journal of the Speleological Society of Korea
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• v.20 no.21
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• pp.34-43
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• 1989

Cheju island is situated at about 60km south of southern most tip of the Korean peninsula. Its shape is an ellips with size of 80*40$\textrm{km}^2$, and it is characterized by a symmetrical form whose peak is Mt. Halla(1950m). Major chemical composition of the rock samples from Manjang gul cave is determined by XRF using the fundamental parameter method consisting of fully auto quantitative analysis, semi quantitative analysis (order estimation) and group quantitative analysis. Judging from chemical composition (SiO$_2$ = 53.07Wt％, Fe$_2$O$_3$ = 11.34Wt％, MgO=6.48Wt％, Na$_2$O=3.07Wt％, $K_2$O=1.05Wt％), this rocks from the Manjang gul cave are also determined. The discrepancy of K-Ar ages is found. They are 0.03 Ma and 0.42Ma, respectively. This paper describes some problems experienced in dating young volcanic rocks and then discusses chemical composition, X-ray fluorescence analysis and the age of the formation of a lava tunnel such as Manjang gul cave in cheju Island.

• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.36-43
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• 2008

Many plutonic rock fragments of granitic composition were collected from the Deception Island. We obtained K-Ar ages of $62.5{\pm}1.2\;Ma$ and $140.7{\pm}2.7\;Ma$ from the two samples. Such result contradicts the general belief that most of the volcanic rocks of Deception Island are products of very recent activities and their maximum age does not exceed 200 ka. On the other hand, Mesozoic to Cenozoic rocks produced by subduction-related active magmatism have been reported from both South Shetland Islands and Antarctic Peninsula, located to the north and south of the Deception Island respectively. Also, various kinds of plutonic rocks with granitic composition are distributed widely. Therefore, plutonic rock fragments with granitic composition discovered from the Deception Island seem to indicate their derivation by capturing granitic crustal material underlying volcanic edifice during the volcanic activities, instead of differentiation from magmas related with recent volcanism. Ages and rock types of the plutonic rock fragments suggest arc-related origin just as adjacent South Shetland Islands and Antarctic Peninasula.

• The Journal of the Petrological Society of Korea
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• v.15 no.2 s.44
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• pp.72-80
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• 2006

We report new K-Ar ages of volcanic rocks from Ulleung-do and Dok-do islands located at the middle of the Korea Sea; $3.67{\pm}0.40\sim1.89{\pm}0.29$ Ma for the Dok-do and $8.07{\pm}0.39\sim0.51{\pm}0.07$ Ma for the Ulleung-do. Such ages reveal that igneous activities of both Dok-do and Ulleung-do extend longer than previously reported. It is likely that igneous activity of Ulleung-do started as early as $8.07{\pm}0.39$ Ma which is much older than age known currently, and latest eruption and intrusion of trachyte of Dok-do lasted until $1.89{\pm}0.29$ Ma, which overlaps previously reported igneous activity of Ulleung-do. However, it seems that the main volcano-building stage of Ulleung-do started after 2.7 Ma and igneous activities of Dok-do were finished mostly before then, which suggests that Dok-do was farmed before Ulleung-do in the respect of main stages of volcano-building. Such explanation agrees well with the hypothesis that southeastern seamounts, Dok-do and Ulleung-do were sequentially generated by relatively fixed hotspot.

• Journal of the Korean earth science society
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• v.28 no.6
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• pp.733-742
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• 2007

Petrological, mineralogical, and geochemical analyses were carried on the paleolithic obsidian implements excavated at Wolseongdong, Daegu, Korea. The obsidians has a homogeneous glassy texture that can be observed in a typical obsidian formed from a rapid cooling of silicic magma. Major element composition of the obsidians represent calc-alkaline series. Comparing those with other obsidians from domestic local excavation sites, Mt. Baekdu, and Kyusu of Japan, the Wolseongdong obsidians show similar element distribution pattern with others in spite of small difference in trace and rare Earth element contents. Sr isotopes of the obsidians considerably differ from those of the obsidians from southern part of the Korean Peninsula or from Mt. Baekdu. K-Ar age is approximately 30 Ma, which is much older than Mt. Baekdu (10 Ma). Therefore, considering the characteristics of obsidians found in the Korean Peninsula including mineralogy, petrology, trace element, and isotopes chronology, the obsidians can be divided into four groups: Mt. Baekdu, southern part of Korea (Kyusu of Japan), middle part of Korea, and Wolseongdong region. These groups suggest a possibility of more than four different origins of the obsidians found in the Korean Peninsular.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.205-214
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• 2005

Some Quaternary faults developed in the eastern block of the Ulsan fault are Gaegok 1, Gaegok 2, Singye, Madong, Wonwonsa and Jinhyeon faults, which are characterized by thin gouge and narrow cataclasitic tones. This study was performed to emphasize the role of mineral alteration and microtexture in response to hydrothermal alteration of fault gouges during fault activity, using XRD, EPMA, BSE (backscattered electron image), and K-Ar age dating methods. Alteration minerals in fault gouges were formed in the age range of $44.3\~28.9Ma$ by hydrothermal alteration attributed to fault activity. XRD results show that fault gouges consist predominantly of clay minerals, quartz and feldspars. Clay minerals formed in the gouge zones are mainly composed of smectite with trace chlorite, illite and kaolinite. The evidence to support the hydrothermal alteration of preexisting minerals due to fault activity are easily recognized at the host rocks in contact with gouges zones. Injected gouge and calcite veins indicate that they were originated from multiple deformation by repeated fault activity. Gouge with green or greenish grey color, for example Jinhyeon fault, contains higher $Al_2O_3$ and lower MgO and CaO compared to those with reddish color. Various colors of fault gouge are intimately related to the chemical compositions of main constituent mineral as well as mineral assemblage.