• Economic and Environmental Geology
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• v.56 no.5
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• pp.547-555
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• 2023

Due to enhanced precision in uranium isotope measurements with MC-ICP-MS, there has been a surge in studies concerning the naturally occurring uranium isotope ratio (²³⁸U/²³⁵U) and its associated fractionation processes. Several researchers have highlighted that the ²³⁸U/²³⁵U ratio, previously assumed to be constant, can vary by several per mil depending on different natural fractionation processes. This review paper outlines the uranium isotope values (δ²³⁸U) for major terrestrial reservoirs and their variations. It discusses the range of δ238U values and uranium isotope fractionation seen in uranium ore deposits, based on deposit type and ore-forming conditions. In conclusion, this paper emphasizes the importance of studies on uranium ore deposits. Such deposits serve as natural simulation models vital for designing high-level radioactive waste repository sites.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.384-387
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• 2004

강원도 지역 탄산수에 대해 혼합에 의한 용존 희유원소의 거동특성 및 탄산염 침전물 형성에 따른 REE 분별작용을 살펴보았다. 탄산수들은 화학적으로 $Na-HCO_3형,\; Ca-Na-HCO_3형\; 및\; Ca-HCO_3$형으로 구분되며, 동위원소조성도 유형에 따라 명확히 구분되는 특징을 보인다. 지화학 및 동위원소 자료의 해석 결과, $Na-HCO_$형 탄산수는 지하심부에서 심부 기원 $CO_2$의 공급에 의해 형성된 반면, 다른 두 유형의 탄산수들은 $Na-HCO_$ 형 탄산수와 천부지하수 간의 혼합에 의해 생성되었음을 지시하였다. 탄산수 내 용존 REE 함량은 물 유형에 따라 변화하지만, ∑REE 함량은 TDS, pH, alkalinity, $\delta^{18}O$$\delta^{18}O$ 및 tritium 함량과 좋은 상관성을 보여주어, 천부 지하수와의 혼합된 특징을 나타내었다. Na-HCO$_3$형 탄산수의 용존 REE 패턴은 강한 HREE 부화를 보여주어 이른바 'S-shape'을 나타내는 반면, $Na-HCO_$ 형은 분산되어 있으며 LREE 부화를 보여주었다. $Ca-Na-HCO_3$형은 약한 HREE 분화 패턴을 보여주었다. 탄산수로부터 침전된 침전물과 침전물을 제거한 잔류물의 REE 패턴은 원 탄산수와 거의 유사한 형태를 보여주어, 탄산염 침전물과 잔류물 간의 REE 분별작용은 일어나지 않았음을 나타낸다.지 않았음을 나타낸다.

• Proceedings of the KSEEG Conference
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• 2007.04a
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• pp.605-605
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• 2007

• Proceedings of the Mineralogical Society of Korea Conference
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• 2001.06a
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• pp.132-132
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• 2001

옥천변성대의 충주-황강리 지역내 앰피볼라이트의 기원암은 염기성 화성암으로 쏠레이아이트 계열의 변이질암에 속한다. Fe $O^{*}$/MgO값의 변화에 대하여 분별작용에 의해 영향을 받는 주성분 원소와 미량원소들의 변화를 보게되면 Ti $O_2$, Fe $O^{*}$와 불호정성 원소(incompatible element)인 Zr, Nb, Hf, Ta, Th 등은 분별작용동안 증가하는 반면 호정성 원소(compatible element)인 MgO, $Al_2$ $O_3$, Ni, Cr 등은 감소하는 경향을 보여주고 있다. Fe $O^{*}$/MgO, Ti $O_2$ 그리고 Fe $O^{*}$는 심해성 쏠레이아이트 영역으로부터 분화된 경향을 나타내 주고 있다. Ni, Cr은 Fe $O^{*}$/MgO값의 증가에 따라 급속히 감소하며 안정한 대륙과 해저화산의 영역에 도시되고 있으며 칼크-알칼리(CA)와는 관계가 없고 쏠레이아이트의 영역에서 변화 패턴을 보여주어 앰피볼라이트가 활동적인 대륙연변부의 지구조 환경보다는 안정한 대륙이나 해저화산과 관계가 더 있음을 시사한다. 경휘토류 원소(LREE)는 중휘토류 원소(HREE)에 비해 더욱 부화된 특성을 띠고 원자번호가 증가하면서 표준화된 휘토류 원소패턴의 경사가 점차 감소하는 경향을 보여주고 있다. 대부분의 시료들은 큰 Eu이상치를 갖고 있지 않아 마그마 정출 과정동안 사장석의 분별작용이 거의 수반되지 않았음을 지시하고 전체적인 휘토류 원소의 패턴은 거의 평행하게 나타나므로 기원 마그마가 유사함을 의미하고 있다. 비유동성 원소를 이용한 여러 판별도표들을 통해서 본암은 대륙성 현무암질암으로서 판내부 환경에서 유래되었으며 대륙내부 열곡의 알칼리 현무암과 대륙성 현무암 영역에 속하는 것으로 보아서 대륙지각내 열곡작용과 같은 장력운동에 수반되어 생성된 것임을 시사해 주고 있다. 앰피볼라이트의 지각혼성화를 평가하기 위해 이에 필요한 몇 개의 지화학적 매개변수를 계산한 결과 La/Ta, La/Nb, Nb/Th들의 값이 오염 안된 마그마의 값을 지시해 주어 본암이 지각혼성화 작용을 받지 않은 것으로 나타났다. 대부분의 시료들은 P-타입 MORB의 영역에 속하며 소수의 시료가 T-타입 MORB의 영역에 도시되고 있어 본 앰피볼라이트의 생성에는 양적으로 다른 두 가지의 유사한 마그마가 수반된 것으로 추정된다. 것으로 추정된다.

• Economic and Environmental Geology
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• v.26 no.3
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• pp.363-370
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• 1993

Various sizes of dolerite sills occur in the Mungyong area, one of well-exposed areas in Okchon belt. All of previous geochemical studies concluded that chemical variations of basic rocks, so-called Sangnae-ri amphibolite, result from the fractional crystallization. The second sill, which is a well differentiated one in the Sangnae-ri area, displays systematic compositional variation associated with gradual change of grain size in vertical sections. In order to clarify the chemical variation in the sill, whether chemical composition of each part of the sill is appropriately derived from the original liquid (represented by the average composition) by addition or subtraction of initial phenocystic minerals are tested(Iwamori program, 1989). According to the calculation, it is shown that major vertical chemical variation of the sill resulted from the accumulation of phenocrysts(olivine, clinopyrxoene, plagioclase, titanomagnetite) which already existed at the time of emplacement or formed just after the emplacement.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.121-138
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• 2018

We have examined the petrotectonic setting and magmatic evolution from petrochemical characteristics of major and trace elements for the Cretaceous volcanic rocks in and around the Mireukdo Island. The volcanic rocks, can be devided into Jusasan, Unmunsa, Yokji and Saryang subgroups on the ascending order, are classified as basalt, basaltic andesite, andesite, dacite and rhyolite on TAS diagram. Petrochemical data show that the rocks are calc-alkaline series, and suggest that erupted earlier medium-K series and later high-K series. The volcanic rocks provide a case in which the calc-alkaline magma are formed, not only from separate protoliths, but following separate paths from source to surface. Earlier and later subgroups take different paths to the surface respectively, and are emplaced in the shallow crust as a series of discrete magma chambers through the volcanic processes. After emplacement, each chamber evolves indepently through fractional crystallization with a little assimilation of wall rock. The volcanic rocks have close petrotectonic affinities with orogenic suite and subduction-related volcanic arc. The rhyolitic magma can be derived from calc-alkaline andesitic magma by fractional crystallization with crustal assimilation, which may be derived from a partial melt of peridotite in the upper mantle.

• The Journal of the Petrological Society of Korea
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• v.5 no.2
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• pp.188-199
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• 1996

Boeun granodiorite, which intruded into the metasedimentary rocks of the Ogcheon Group, show chemical natures of metaluminous and calc-alkaline. Generating and emplacing environment of the Boeun granodiorite would have been a active continental margin. Comparing to the contemporaneous Inje-Hongcheon granodiorite in the Gyeonggi massif, the Boeun granodiorite seems likely to have formed under more immature continental arc environment. Compositional changes of major, trace and rare earth elements in granodiorite and felsic dyke are not certain to indicate crystallization differentiation. From this fact, the simple fractional crystallization model would be in question to explain the magma process which controlled the formation of the Boeun granitic mass. The model calculations for Rayleigh fractionation, fractionation with variable major-component composition, assimilation-fractional crystallization (AFC) were carried out to examine the magma process of the mass. The results of former two models do not agree with the compositional variations in the mass. The AFC model can be, however, applied to the magma process. The conditions for AFC process are (1) composition of assimilated wallrock is similar to that of primary magma. (2) assimilating rate is similar to crystallizing rate, and (3) mass of assimilated wallrock is about 10% of that of the magma. These conditions deny a possibility that the assimilated wallrock was the metasedimentary rocks of the Ogcheon Group. This indicates that after having experienced the assimilation process in deeper crust, the granodiorite magma intruded into the Ogcheon group. Every model calculating suggests that the felsic dyke was differentiated not from the granodiorite magma, but from a different source magma.

• 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.

• The Journal of the Petrological Society of Korea
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• v.17 no.2
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• pp.57-82
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• 2008

The volcanic sequence of the late Cretaceous Moonyu volcanic mass which distributed in the southwestern part of Ryeongnam massif, can be divided into felsic pyroclastic rocks, andesite and andesitic pyroclastic rocks, rhyolite in ascending order. The earliest volcanic activity might commence with intermittent eruptions of felsic magma during deposition of volcaniclastic sediments. Explosive eruptions of felsic pyroclastic rocks began with ash-falls, to progressed through pumice-falls and transmitted with dacitic to rhyolitic ash-flows. Subsequent andesite and andesitic pyroclastic rocks were erupted and finally rhyolite was intruded as lava domes along the fractures near the center of volcanic mass. Petrochemical data show that these rocks are calc-alkaline series and have close petrotectonic affinities with subduction-related continental margin arc volcanic province. Major element compositions range from medium-K to high-K. Petrochemical variation within the volcanic sequence can be largely accounted for tractional crystallization processes with subordinate mixing. The most mafic rocks are basaltic andesite, but low MgO and Ni contents indicate they are fractionated by fractional crystallization from earlier primary mafic magma, which derived from less than 20% partial melting of ultramafic rocks in upper mantle wedge. Based on the stratigraphy, the early volcanic rocks are zoned from lower felsic to upper andesitic in composition. The compositional zonation of magma chamber from upper felsic to lower andesitic, is interpreted to have resulted from fractionation within the chamber and replenishment by an influx of new mafic magma from depth. Replenishment and mixing is based on observations of disequilibrium phenocrysts in volcanic rocks. REE patterns show slight enrichment of LREE with differentiation from andesite to rhyolite. Rhyolite in the final stage can be derived from calc-alkaline andesite magma by fractional crystallization, but it might have underwent crustal contamination during the fractional crystallization.

• Economic and Environmental Geology
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• v.46 no.5
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• pp.375-390
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• 2013

The Kenticha rare-element (Ta-Li-Nb-Be) mineralized zone is located in ophiolitic fold and thrust complex of southern Ethiopia and was firstly discovered by joint exploration program of Ethiopia-Soviet in 1980s. It includes Dermidama, Kilkele, Shuni Hill, Kenticha, and Bupo pegmatites from south to north. The Kenticha pegmatite intruded parallel to NS-striking serpentinite and talc-chlorite schist, and is exposed approximately 2 km length and 400-700 m width. The Kenticha pegmatite is internally zoned and subdivided into lower quartz-muscovite-albite granite, intermediate muscovite-quartz-albite-microcline pegmatite, and upper spodumene-quartz-albite pegmatite, based on their mineral assemblage. The major, trace elements (e.g., Rb, Li, Nb, Ta, and Ga), and element ratios (e.g., K/Rb, Nb/Ta, Mg/Li, and Al/Ga) suggest that the fractionation and solidification of pegmatite have progressed from the lower towards upper pegmatite. In contrast, unlike general magmatic fractionation, Mg/Li ratios of the Kenticha pegmatite tend to be increased towards the upper pegmatite. It may result from post-magmatic hydrothermal alteration and/or interaction with upper ultramafic rock. Rare-element mineralization in Kenticha pegmatite concentrates on the upper pegmatite, which contains up to 3.0 wt % $Li_2O$, 3,780 ppm Rb, 111 ppm Cs, 1,320 ppm Ta, and 332 ppm Nb. Ore minerals in Kenticha pegmatite mostly include tantalite, spodumene, and lepidolite, and tantalite has an association with coarser quartz-spodumene and relatively fine sacchroidal albite. The tantalite is classified into Mn-tantalite as a function of $Mn^*[Mn/(Mn+Fe)]$ and $Ta^*[Ta/(Ta+Nb)]$ values. Its compositions ($Mn^*$, $Ta^*$, and Nb/Ta) between coarse and fine tantalites are different and the former is strongly enriched in Ta and depleted in Nb compared to latter one. In conclusion, rare-element mineralization in the Kenticha pegmatite may has occurred in the latest stage of magmatic fractionation.