• Geosciences Journal
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• 제22권6호
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• pp.921-938
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• 2018

The Motzfeldt intrusions in the Gardar Province, southern Greenland, split into syenitic plutonic and hypabyssal rocks, in which the latter include ring dykes and sheet intrusions. Sheet intrusions, considered as the source for rare earth elements (REE) and high field strength elements (HFSE), comprise sheets of peralkaline microsyenite (SPM), syenitic pegmatite (SP), and peralkaline microsyenite (PM). SP exhibits extremely high concentrations of REE and HFSE, which are positively correlated with increasing alkalinity from early towards late intrusion, caused by magmatic processes. In contrast, some of the SPM and PM are also significantly enriched in REE and HFSE, caused by post-magmatic fluids. The REE- and HFSE-rich phases in SP consist mainly of zircon and allanite with smaller amounts of pyrochlore in pseudomorph from the inferred eudialyte, whereas some of the PM and SPM consist of pyrochlore, REE-carbonate, and zircon in the matrix. The zircon grains in the Motzfeldt Sø Formation (MSF) syenite occur in interstitial spaces, exhibiting an association with magnetite and a bipyramidal form in texture. They are characterized by a highly fractured and embayed rim. Zircons from PM and SP are clearly enriched in Fe, Al, Ca, Na, Y, P, Hf, Y, P, Nb, Ta, and REE, and are depleted in Zr and Si in comparison with magmatic zircon. They also show a clear trend of higher LREE/HREE and $Eu/Eu^{\star}$ ratios, and lower $Ce/Ce^{\star}$ ratios, which define them as typical hydrothermal zircons. In contrast, zircons from the MSF syenite show a relatively lower LREE/HREE ratio and Eu and Ce anomalies of a similar magnitude compared with those from SP and PM. The occurrence and mineral composition of the zircon suggest that post-magmatic fluids have played an important role in the remobilization of REE and HFSE as well as the primary concentration of REE and HFSE, caused by magmatic processes.

• 자원환경지질
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• 제32권5호
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• pp.421-434
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• 1999

Gas and chemical compositions of fluid inclusions in quartz some of Au-Ag, Pb-Zn-Cu and W-Mo mineral deposits in South Kores were analyzed to interpret the sources of ore fluid and the depositional condition of ore minerals in base-metal ore deposits. Fluid inclusions in quartz from the gold and silver mines are characterized by $CO_2$ rich fluids which have a wide range in $CH_4 \;and\; CO_2$ contents ($CH_4/CO_2$=0.001-0.225). The $CO_2$ rich but $CH_4$-poor nature of the fluid reflects the high fo2 condition during the mineral precipitation. The C2H6 is detected in hydrothermal quartz vines in metasedimentary rocks from the Jeonjoo-il, Youngbokari and Taechang mines. The $CH_4 /CO_2$ rations in W-Mo bearing quartz veins range from 0.005 to 0.214, which is similar with those in Au-Ag mines. However, skarn formation stage. Fluid inclusions, A relatively good correlation between Na and Cl contentrations reflects varible salinity in the fluid inclusion, it is suggested that the chemistry of promary magmatic hydrothermal fluids has changed during post-magmatic alteration and/or wall rock alteration processes. The content of gas compositions also depends on the kinds of country rocks, supporting above conclusion.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2009년도 특별 심포지엄
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• pp.57-65
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• 2009

Selection of good mineralized area is a combination of the integration of all the available geo-scientific (i.e., geological, geochemical, and geophysical) information, extrapolation of likely features from known mineralized terrenes and the ability to be predictive. The time-space relationships of the hydrothermal deposits in the East Asia are closely related to the changing plate motions. Also, two distinctive hydrothermal systems during Mesozoic occurred in Korea: the Jurassic/Early Cretaceous deep-level ones during the Daebo orogeny and the Late Cretaceous/Tertiary shallow geothermal ones during the Bulguksa event. Both the Mesozoic geothermal system and the mineralization document a close spatial and temporal relationship with syn- to post-tectonic magmatism. The Jurassic mineral deposits were formed at the relatively high temperature and deep-crustal level from the mineralizing fluids characterized by the relatively homogeneous and similar ranges of ${\delta}^{18}O$ values, suggesting that ore-forming fluids were principally derived from spatially associated Jurassic granitoid and related pegmatite. Most of the Jurassic auriferous deposits (ca. 165-145 Ma) show fluid characteristics typical of an orogenic-type gold deposits, and were probably generated in a compressional to transpressional regime caused by an orthogonal to oblique convergence of the Izanagi Plate into the East Asian continental margin. On the other hand, Late Cretaceous ferroalloy, base-metal and precious-metal deposits in the Taebaeksan, Okcheon and Gyeongsang basins occurred as vein, replacement, breccia-pipe, porphyry-style and skarn deposits. Diverse mineralization styles represent a spatial and temporal distinction between the proximal environment of sub-volcanic activity and the distal to transitional condition derived from volcanic environments. However, Cu (-Au) or Fe-Mo-W deposits are proximal to a magmatic source, whereas polymetallic or precious-metal deposits are more distal to transitional. Strike-slip faults and caldera-related fractures together with sub-volcanic activity are associated with major faults reactivated by a northward (oblique) to northwestward (orthogonal) convergence, and have played an important role in the formation of the Cretaceous Au-Ag lode deposits (ca. 110-45 Ma) under a continental arc setting. The temporal and spatial distinctions between the two typical Mesozoic deposit styles in Korea reflect a different thermal episodes (i.e., late orogenic and post-orogenic) and ore-forming fluids related to different depths of emplacement of magma (i.e., plutonic and sub-volcanic) due to regional changes in tectonic settings.

• 자원환경지질
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• 제40권5호
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• pp.517-535
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• 2007

중생대부터 한반도에서 나타나는 열수계는 쥐라기/전기 백악기 (약 $200{\sim}130$ Ma) 심부지질환경과 관련된 조산대형 열수계와 후기 백악기/제3기 (약 $110{\sim}45$ Ma) 천부지질환경의 후조산대형 열수계로 구분된다. 이러한 열수계에 수반된 금속광화작용은 시 공간적 관점에서 조산대형 및 후조산대형 화성활동의 특성을 반영하고 있다. 그리고 각 유형 광화유체의 ${\delta}^{18}O_{H2O}$는 쥐라기 조산대형 광상에 비하여 후기 백악기 후조산대형 광상에서 현저한 조성변화를 보이고 있다. 즉, 조산대형 광상은 경기 영남 육괴에 배태되며, 심부 지질조건에서 균질한 $^{18}O$-부화된 고온성 광화유체로부터 진화된 열수충진형 금광상과 희유금속 광상으로 인접한 대보화강암체 또는 분화된 페그마타이트로부터 유입된 마그마수 또는 일부 변성수로부터 유도되었다. 반면에 후기 백악기 광상은 태백산분지, 옥천 지향사대 및 경상분지의 전 지역에 걸쳐 광범위하게 산출되며, 철합금, 비철금속 및 귀금속 광상의 열수충진형, 열수교대형, 각력 파이프형, 반암형, 스카른형 광상과 같은 다양한 광상유형으로 배태되고 있다. 이러한 다양한 유형의 광화유체는 물-암석 반응에 따라 산소 동위원소비$({\delta}^{18}O)$가 폭 넓게 변화하는 산소 편이의 전형적인 특징을 보이는 반면 수소 동위원소비$({\delta}D_{H2O})$는 비교적 균질한 조성특징을 나타내고 있다. 또한 근지성 유형 광상의 산소 동위원소비는 부화된 경향을 보이지만, 점이성/원지성 유형 광상에서는 전반적으로 폭 넓게 변화하며 부분적으로 결핍된 특징을 보이고 있다. 즉 근지성 유형의 Cu(-Au)또는 Fe-Mo-W 광상에서는 탈가스화작용 이후에 나타나는 마그마수의 전형적인 특징을 보이는 반면, 다금속 광상과 귀금속 광상은 점이성 또는 원지성 유형으로 지표수(또는 순환수)의 혼입이 우세한 경향을 보인다.

• 자원환경지질
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• 제30권5호
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• pp.395-406
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• 1997

Some RE (Zr, Nb, REE) ore deposits are located in the middle part of the Korean peninsula. Geotectonically, the RE ore deposits situated on the Kyemyeongsan Formation of northern margin of the Okcheon geosynclinal belt and in the transitional zone between Kyeonggi massif and Okcheon belt. The rare metal deposits distributed in Kyemyeongsan Formation which consists of schist and alkaline granite. The alkali granite has suffered extensive post-magmatic metasomatism and hydrothermal processes. The ore contains mainly Ce-La, Ta-Nb, Y, Y-Nb, Ti-Nb-(U), Nd-Th group minerals. Fergusonite, one of Nb-Y rich REE minerals belonging to the A-B oxides, is most common mineral in the rare metal deposits. The fergusonite bearing rocks may be devided into four types by occurrence features and mineral association, that is, zircon type, allanite vein, feldspar type, and fluorite type. Fergusonites show wide variations in optical properties, due to part of differences in their chemical composition (depending on the types), but also the degree of crystalinity of the individual specimens. Fergusonite metamicts enclosed in biotite are generally surrounded by well developed pleochroic haloes. Usually, fergusonite is accompanied with zircon and other REE-bearing minerals. Petrographical and chemical data are presented for fergusonites which collected different types. $Nb_2O_3$ and $Y_2O_3$ contents range from 48.51 to 53.01 wt.% and 29.18 to 42.02 wt.% respectively. Also, $ThO_2$, (1.83~6.93), $UO_2$, (0.17~2.84), ${\sum}RE_2O_3$ (except to Y) (1.11~8.73), and $TiO_2$, (0.19~1.19 wt.%) contents show variational compositions according to fergusonite types. The ${\sum}RE_2O_3$ of fergusonites are positive relation with $Y_2O_3$ and negative relaton with $ThO_2$ and $({\sum}{RE_2O_3}-{Y_2O_3})$. The $Nb_2O_3$ is sightly negative relation with $Ta_2O_3$. Back-scattered electron microscope images (BEI) of fergusonite show the mineral composition and textural feature is very complicated. The variation of Nb, Th and REE content of fergusonite and the modes of occurrence of mineral, suggests that REE may have been mobilized during the circulation of hydrothermal fluids related to contact metamorphism (metasomatism). The chemical variation of the fergusonites with occurrences and mineral association can be related to metasomatism of alkaline fluid was probably the dominant ore-forming process in Chungju district.