• Journal of Soil and Groundwater Environment
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• v.18 no.1
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• pp.36-45
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• 2013

We analyzed natural radionuclides in 80 wells in volcanic rock areas and investigated environmental characteristics. Uranium and radon concentrations ranged from ND to $9.70{\mu}g/L$ (median value: 0.21) ${\mu}g/L$, 38~29,222 pCi/L (median value: 579), respectively. In case of gross-${\alpha}$, 26 samples exceeded MDA (minimum detectable activity, < 0.9 pCi/L) value and the activity values ranged from 1.05 to 8.06 pCi/L. The radionuclides concentrations did not exceed USEPA MCL (maximum contaminant level) value of Uranium ($30{\mu}g/L$) and gross-${\alpha}$ (15 pCi/L). But Rn concentrations in 4 samples exceeded USEPA AMCL (Alternative maximum contaminant level, 4,000 pci/L) and one of them showed a significantly higher value (29,222 pCi/L) than the others. The levels of uranium concentrations in volcanic rock aquifer regions were detected in order of andesite, miscellaneous volcanic rocks, rhyolite, basalt aquifer regions. Radon, however, was detected in order of miscellaneous volcanic rocks, rhyolite, andesite, basalt aquifer regions. The correlation coefficient between uranium and radon was r = 0.45, but we found that correlations of radionuclides with in-situ data or major ions were weak or no significant. The correlation coefficient between the depth of wells and uranium concentrations was a slightly higher than that of depth of wells and radons. Radionuclide concentrations in volcanic rock aquifers showed lower levels than those of other rock aquifers such as granite, metamorphic rock aquifers, etc. This result may imply difference of host rock's bearing-radioactive-mineral contents among rock types of aquifers.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.571-577
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• 1995

Several acid-sulfate clay deposits associated with silicic magmas occur in the Haenam area of the southwestern part of Korea. Geology of the studied area consists of tuffs, granitic rocks, quartz porphyry, rhyolite, andesite and sedimentary rocks. The granitic rocks and quartz porphyry intruded tuffs and sedimentary rocks. The rhyolite and tuffs around the mines have undergone hydrothermally weak or strong alteration. Gold contents with major and trace elements have been determined for a total of sixty-seven specimens of fresh igneous rocks, wall rocks and minerals such as dickite and alunite by graphite furnace atomic absorption spectrometer and inductively coupled plasma. Gold is enriched in the alunite vein and the silicified zone, but is depleted in dickites and hydrothermally altered rocks with dickite of the Seongsan deposit. Gold is especially concentrated near the faults or conjunction area of two faults. High content of gold is shown in the mineral assemblages of alunitequartz- pyrite in the alunite vein and silicic zone of the Seongsan deposit compared with that of minerals and rocks from another deposits distributed in the studied area. Gold content in tuffs and dickites with pyrite is generally low. Gold content in silicified tuff tends to show positive correlations with content of As, Hg and Sb. Variation trends of Cd, Hg and Sb are similar to those of gold content. From the result of gold content variations, gold may be transported and concentrated by mineralizing solutions ascending along the cracks like fault. Therefore, it is important to survey alunite vein and silicified zone at the conjunction of faults, and to analyze pathfinder elements such as As, Hg and Sb for geological and geochemical exploration of gold in the studied deposits.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.603-612
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• 1997

Cretaceous sedimentary-volcanoclastic formations of the Kyeongsang Supergroup were intruded by granitic rocks in the late Cretaceous and early Tertiary. In the Euiseong and Shinryeong area, these intrusives have various compositions including gabbro, diorite，biotite granite and feldspar porphyry. Associated volcanic rocks consist of two chemically distinct types: the bimodal suite of basalt and rhyolite in the Keumseongsan caldera, and the felsic suite of andesite and rhyolite in the Sunamsan-Hwasan calderas. Most rocks are subalkaline, and follow a typical differentiation path of the calc-alkaline magma. The granitic rocks can be distinguished chemically from the volcanics by high Zr/Y ratios. Differences in Zr/Y and K/Y ratios between the two volcanic suites can be accounted for by mantle source and fractionation. Chondrite-normalized trace element abundances of granitic rocks are depleted in Th and K, whereas those of the Keumseongsan rhyolites are depleted in Sr and Ti. Rb, La and Ce is enriched in rhyolites of the Sunamsan-Hwasan calderas. $Rb-SiO_2$ and Rb-Y+Nb discrimination diagrams suggest that the intrusives and volcanics have a volcanic arc setting. K-Ar ages indicate four plutonic episodes : diorite (89 Ma), granite (66~62 Ma), granite and porphyry (55~52 Ma) and gabbro (52~45 Ma), and two volcanisms : bimodal basaltic and rhyolitic volcanism (71~66 Ma) in the Keumseongsan caldera, and felsic andesitic and rhyolitic volcanism (61~54 Ma) in the Sunamsan-Hwasan calderas. Geochemical and age data thus suggest that the igneous rocks are related to several geologic episodes during the late Cretaceous to early Tertiary.

• Journal of the Korean earth science society
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• v.21 no.1
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• pp.67-80
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• 2000

We studied petrological and geochemical characteristics of the Mesozoic volcanic rocks in the Da Hinggan Ling area northeast China, and discussed tectonic settings and origin of the Mesozoic volcanic rocks in northeast Asia. Volcanic rocks in Da Hinggan Ling area are composed of alkaline to subalkaline basalt-basaltic andesite-andesite-dacite-rhyolite, showing typical BAR(basalt-andesite-rhyolite) association. However, most of the volcanic rocks are basaltic and rhyolitic in composition, and andesitic rocks are relatively rare, which shows bimodal characteristics. Rb, Ba, Th and other incompatible element contents in the volcanic rocks are enriched, but the contents decrease with increasing the compatibility. REEs are fractionated and REE patterns of volcanic rocks are characterized by a high LILE/HFSE. On the tectonomagmatic discriminant diagram of Hf-Th-Nb, they fall into the fields for subduction-related destructive plate margin basalts and its differentiates. We suggest that the tectonomagmatic setting of Da Hinggan Ling area was located at the continental margin arc related with subduction environment during the Mesozoic time or may be derived from mantle plume contaminated geochemically from subducting slabs, although it is, at present within the Asia continent.

• The Journal of the Petrological Society of Korea
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• v.7 no.3
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• pp.161-176
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• 1998

There are exposed Samrangjin Tuff and intracaldera intrusions, of which rhyolitic rocks emplaced as postcollapsed central and ring intrusions within the Samrangjin caldera, and fine-grained granodiorite and biotite granite as regional tectonic intrusions nearby. The Samrangjin Tuff and the rhyolitic rocks are of a single Samrangjin magmatic system. Flow-banded rhyolite among rhyolitic rocks was emplaced in the outer part of the ring intrusions, rhyodacite in the inner part of the eastern ring, and porphyritic dacite and dacite porphyry in the inner part of the northwestern ring. Totally the Samrangjin Tuff and the rhyolitic rocks range from rhyolite to dacite in chemical composition. The Rb-Sr isotopic data of the Samrangjin Tuff and the rhyolitic rocks yield an age of $80.8{\pm}1.5(2{\sigma})$ Ma with the initial $^{87}Sr/^{86}Sr$ ratio of $0.70521{\pm}0.00010(2{\sigma})$. The continuous compositional zonations generally define a large stratified magma system in the postcollapse magma chamber. The Sr isotopic data suggest that the compositional zonations might have resulted from the fractional crystallization of a parental dacitic magma.

• Journal of the Korean earth science society
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• v.26 no.7
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• pp.630-639
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• 2005

The purpose of this study was to investigate the classifying ability of the igneous rocks with the naked eye for 36 preservice science teachers. For this, we selected six specimens of igneous rocks that consisted of rhyolite, andesite, basalt, granite, diorite, and gabbro, and performed the questionnaire with them. Preservice science teachers needed the average of 3 tools to classify the rocks. Most of the selected tools were loupe, streak plate, hammer and Mohs’ hardness scale. Many preservice science teachers selected basalt and granite samples to classify igneous rocks among 6 kinds of the rocks which were exhibited. However, the results of the identification with the naked eye showed that the right answer rate was significantly different based on what rock sample had been selected. Nobody gave the right answer among 10 students who chose the rhyolite sample, but all of 36 students who picked the basalt sample answered correctly. And $62\%$ of 8 students who chose the andesite sample, 62% of 32 student choosing granite, $7\%$ of 13 students choosing diorite and $44\%$ of 9 students choosing gabbro were correctly answered. In identifying igneous rock samples with the naked eye, most subjects relied on vesicular texture to basalt, and they used textural, color and empirical characters to granite. But, some felt more or less difficulty to distinguish between intermediate and light colors and to recognize porphyry.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.166-184
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• 1997

The Wondong caldea is a deeply eroded structure that offers spectacular exposures through the core and margins of a resurgent caldera. The Wondong Tuff and the postcollapse intrusions range from medium-silica rhyolite to rhyodacite in composition and the postcollapse lava and tuff, preresurgent and resurgent intrusions also range from medium-silica rhyolite to an-desite, which jump to gap dacite composition. The continuous compositional zonations generally define a large stratified magma system in the postcollapse and resurgent magma chamber. Isotopic and trace element evidence suggest that the compositional zonations might have resulted from the differentiations from crystal fractionations of a parental andesitic magma, accompanying a little contamination from the crustal assimilations near the chamber roof and wall. But chemically and isotopically distinct late intusions might have resulted from emplacement of any different magma batch.

• Economic and Environmental Geology
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• v.41 no.3
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• pp.275-286
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• 2008

The Sambo gold deposit located nearby the Cretaceous Hampyeong basin is composed of gold quartz fine vein(the Jija vein) within Cretaceous rhyolite showing $N10{\sim}20W$ trends as well as $N5{\sim}10E$ trending quartz veins(the Pungja, Gwangsan and Pungjaji veins) in Precambrian gneiss. The gold vein typically displays the intermittent and irregular fine veins within rhyolite. Electrum is disseminated in wallrock along the fine cracks as well as coexists with hematite replacing pyrite. Ore-forming fluids from the mineralized vein($H_2O/-NaCl$ system, Th; $340{\sim}200^{\circ}C$, Salinity <2.7 eq. wt.% NaCl) and NE-trending veins($H_2O-NaCl/-CO_2$ system, Th; $400{\sim}190^{\circ}C$, salinity <7.9 eq. wt.% NaCl) are featured by dissimilar physicochemical conditions but their fluid evolution trends(boiling and mixing) are similar with each other. Gold veins of the Sambo deposit filled along NNW-trending tension crack are related to pull-apart basin evolution. Selective gold mineralization of the deposit reflect to dissimilarity between two ore-forming fluid sources. Consequently, gold veining of the Sambo deposit formed at shallow-crustal level and could be categorized into epithermal-type gold deposit related to tensional fractures filling triggered by Cretaceous geodynamics.

• Economic and Environmental Geology
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• v.50 no.6
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• pp.467-476
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• 2017

Volcanic rocks related to the Guamsan cadera, which find in the southeastern Cheongsong, are divided into Volcanic breccia, Guamsan Tuff and Post-collapse intrusions. We determined their eruption, intrusion and caldera-forming timings based on SHRIMP U-Pb zircon dating. The dating results yield earlier eruption age of $63.77{\pm}0.94Ma$ from the lower ash-flow tuff and an later eruption age of $60.1{\pm}1.8Ma$ from the upper ash-flow tuff of the Guamsam Tuff, and intrusion age of $60.65{\pm}0.95Ma$ from the rhyolite ring dyke of the Post-collapse intrusions. The age data suggest that the Guamsan caldera is formed in 60.65~60.1 Ma between eruption of the upper ash-flow tuff and intrusion of the rhyolite ring dyke. The Guamsan cadera exhibits the volcanic processes of a perfect igneous cycle passing from ash-flow eruptions through caldera collapse to ring intrusions during 63.77~60.1 Ma.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.67-87
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• 2010

This article deal with petrotectonic setting and petrogenesis from petrography and chemical analyses of the Cretaceous volcanic and intrusive rocks in the Cheolwon basin. The volcanic rocks are composed of basalts in Gungpyeong Formation, Geumhaksan Andesite, and rhyolitic rocks (Dongmakgol Tuff, Rhyolite and Jijangbong Tuff), and intrusive rocks, Bojangsan Andesite, granite porphyry and dikes. According to petrochemistry, these rocks represent medium-K to high-K basalt, andesite and rhyolite series that belong to calc-alkaline series, and generally show linear compositional variations of major and trace elements with increase in $SiO_2$ contents, on many Harker diagrams. The incompatible and rare earth elements are characterized by high enrichments than MORB, and gradually high LREE/HREE fractionation and sharp Eu negative anomaly with late strata, on spider diagram and REE pattern. Some trace elements exhibit a continental arc of various volcanic arcs or orogenic suites among destructive plate margins on tectonic discriminant diagrams. These petrochemical data suggest that the basalts may have originated from basaltic calc-alkaline magma of continental arc that produced from a partial melt of upper mantle by supplying some aqueous fluids from a oceanic crust slab under the subduction environment. The andesites and rhyolites may have been evolved from the basaltic magma with fractional crystallization with contamination of some crustal materials. Each volcanic rock may have been respectively erupted from the chamber that differentiated magmas rose sequentially into shallower levels equivalenced at their densities.