• The Journal of the Petrological Society of Korea
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• v.20 no.2
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• pp.99-114
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• 2011

Precambrian gneiss complex in the Pyeongchang-Wonju area, which lies west of the Paleozoic sedimentary basin of the Yeongwol-Taebaek area, is being considered as a part of the Gyeonggi massif, but its ages of formation and metamorphic events are not well defined yet. In this study, SHRIMP zircon U-Pb ages were determined from the gneiss complex in the area, We obtained the discrete ages of magmatic (ca. 1960 Ma) and metamorphic (ca. 1860 Ma) events through the interpretation of the SHRIMP data based on the internal structures of zircons. These are almost the same to the ages of main intrusion and metamorphism reported from the Precambrian basements of Gyeonggi, Yeongnam and Nangnim massifs of the Korean Peninsula, Ages of 3200~3300 Ma, 2900 Ma, 2660 Ma, 2430 Ma, 2260 Ma, and 2080~2070 Ma obtained from inherited cores of studied zircons are also very similar to the frequently reported ages from the basement rocks of the Gyeonggi and Yeongnam massifs, Lower intercept age of about 270 Ma calculated from the rim data seems to indicate that the study area suffered from a late Paleozoic metamorphism (Okcheon Orogeny), but we need more reasonable and sufficient data to confirm it. According to the results of this study, it is suggested that the Bangnim group unconformably overlying the gneiss complex was deposited after the Paleoproterozoic granitic magmatism (ca. 1960 Ma) and metamorphism (ca. 1860 Ma).

• Economic and Environmental Geology
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• v.25 no.4
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• pp.447-461
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• 1992

The Jurassic granitoids in the study area are divided into the "Gneissose granodiorite" and the "Daebo granodiorite" (1 : 250,000 Jeonju Geological map, 1973). The term of Geochang granodiorite was used in this study instead of "Daebo granodiorite". These granitoids were studied in terms of microscopic observation, petrochemistry, and zircon morphology. The granitoids are mostly granodiorite. Two kinds of progressive variation can also be recognized in the modal quartz~alkali feldspar~plagioclase triangular diagram; the Gneissose granodiorite is in accordance with the trondhjemitic (low k) trend, and the Geochang granodiorite with the granodioritic trend (medium k). The granitoids belong to the calc-alkaline series, and are classified into the I-type (magnetite series). Plagioclase ($An_{25.1}{\sim}An_{30.9}$) in the granitoids shows generally an oligoclase composition. Biotite has a wider range in (Si, Al) solution than in (Fe, Mg) solid solution. Hornblende occurs in a few thin sections of the Geochang granodiorite, and is plotted in the tschermakite field. The zircon prism shows a long variation between the {110} dominant type and the {100} dominant type in the Geochang granodiorite, but only the {110}={100} type in the Gneissose granodiorite. However, zircon crystals in the granitoids are mostly crystallized in a low-to-medium temperature magma. In the PPEF (Prism- Pyramid-Elongation-Flatness) diagram, the Gneissose granodiorite shows a closed scissors type, the Geochang granodiorite, a opened scissors type. It indicates that the Geochang granodiorite might originate from the mixed magma with crustal materials or pre-existed residual magma which had formed the Gneissose granodiorite.

• Geosciences Journal
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• v.23 no.1
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• pp.1-20
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• 2019

We present data from the Mesozoic Keumkang, Palbong, and Baekhwa granites in Garorim Bay, in the southwestern part of the Gyeonggi massif, South Korea. Using major and trace element concentrations, Sr-Nd-Pb isotopic compositions, and sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages, we aim to constrain the petrogenesis of the granites and explain their origin within a broader regional geological context. SHRIMP U-Pb zircon ages of $232.8{\pm}3.2$, $175.9{\pm}1.2$, and $176.8{\pm}9.8$ Ma were obtained from the Keumkang, Palbong and Baekhwa granites, respectively. The Late Triassic Keumkang granites belong to the shoshonite series and show an overall enrichment in large ion lithophile elements (LILE), a depletion in high field strength elements (HFSE) relative to primitive mantle, compared with neighboring elements in the primitive mantle-normalized incompatible trace element diagram with notable high Ba and Sr contents, and negligible Eu anomalies. The Keumkang granites are typified by highly radiogenic Sr and unradiogenic Nd and Pb isotopic compositions: $(^{87}Sr/^{86}Sr)_i=0.70931-0.70959$, $(^{143}Nd/^{144}Nd)_i=0.511472-0.511484$ [$({\varepsilon}_{Nd})_i=-17.0$ to -16.7], and $(^{206}Pb/^{204}Pb)=17.26-17.27$. The Middle Jurassic Palbong and Baekhwa granites belong to the medium- to high-K calc-alkaline series, and show LILE enrichment and HFSE depletion similar to the Keumkang granites, but exhibit significant negative anomalies in Ba, Sr, and Eu. Furthermore, they have elevated Y and Yb contents at any given $SiO_2$ content compared with other Jurassic granitoids from the Gyeonggi massif. The Palbong and Baekhwa granites have slightly less radiogenic Sr and more radiogenic Nd and Pb isotopic compositions [$(^{87}Sr/^{86}Sr)_i=0.70396-0.70908$, $(^{143}Nd/^{144}Nd)_i=0.511622-0.511660$, $({\varepsilon}_{Nd})_i=-15.4$ to -14.7, $(^{206}Pb/^{204}Pb)=17.56-17.76$] relative to the Keumkang granites. The Keumkang granites are considered to have formed in a post-collisional environment following the Permo-Triassic Songrim orogeny that records continent-continent collision between the North and South China blocks, and may have formed by fractional crystallization of metasomatized lithospheric mantle-derived mafic melts. The Palbong and Baekhwa granites may have been produced from a gabbroic assemblage at pressures of less than ~15 kbar, associated with subduction of the paleo-Pacific (Izanagi) plate at the Eurasian continental margin. Elevated ${\varepsilon}_{Nd}(t)$ values in the granitoids from the southwestern part of the Gyeonggi massif relative to those of the central and northern parts, together with the comparatively shallow depth of origin, imply the presence of an exotic block in the Korean lithosphere.

• The Journal of the Petrological Society of Korea
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• v.13 no.2
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• pp.81-102
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• 2004

The plutonic rocks in Seonsan area are divided into dioritic-syenitic rock, gneissose granite, biotite granite and fine grained biotite granite. These rocks intruded into the Pre-cambrian metamorphic complex and are all covered by the Cretaceous Nakdong formation. According to modal minerals, dioritic-syenitic rock corresponds to quartz monzonite, granodiorite, tonalite fields, whereas all the other plutonic rocks fall in granite field. Petrochemically the dioritic-syenitic rock is lower in SiO$_2$ content, differentiation index and Larsen index than all the other plutonic rocks. About the zircon morphology, dioritic-syenitic rock shows (100) dominant type but other granitic rocks exhibit mixed types between (100) and (110) type. The dioritic-syenitic rock could be crystallized in higher temperature than the other plutonic rocks. The plutonic rocks correspond to calc-alkaline rock series, and belong to I-type granite and mostly magnetite-series in magmatic origin. In plutonic processes, the dioritic-syenitic rock with 5kb vapor pressure could intrude into the metamorphic batement at 17km deep below the surface. Later the gneissose granite with lower 3kb vapor pressure could intrude at 10km deep. Sequentially the biotite granite with 0.7kb could intrude at 2km deep. Finally the fine grained biotite granite with 3kb vapor pressure could intrude at 10km deep.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.209-220
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• 2014

SHRIMP zircon U-Pb age dating is carried out for the Yeongju and Andong granite batholiths intruding the Precambrian metamorphic complex and Paleozoic sedimentary formations within the NE Yeongnam Massif, Korea. Dating of zircons from a hornblende-biotite tonalite and an equigranular biotite granodiorite in the Yeongju granite has yielded ages of ca. 187 Ma and ca. 186 Ma, respectively. Also, dating of zircons from a biotite granodiorite and a very coarse-grained biotite granite in the Andong granite has yielded ages of ca. 182Ma and ca. 186Ma, respectively. These data indicate that the main intrusions of the Yeongju and Andong granite batholiths occur almost at the same age. The oldest age of ca. 194 Ma has been determined on zircons from a hornblende gabbro in the Andong granite, and the youngest age of 175 Ma is obtained from the Chunyang granite pluton, mainly consisting of fine-grained two-mica granite, of the Yeongju batholith. These results indicate that Jurassic Daebo magmatism in the Yeongju-Andong area, NE Yeongnam massif, started early at the Early Jurassic with an intrusion of mafic magma, and followed by an emplacement voluminous granite magma during the middle of the Early Jurassic, and was finalized with the emplacement of relatively small amount of much evolved granite magma at the end of Early Jurassic.

• Economic and Environmental Geology
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• v.56 no.6
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• pp.817-830
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• 2023

This study investigates the age of the surficial rocks in the Arunta region using Uranium-Lead (U-Pb) geochronological dating. Rock samples were collected at four locations, Cattle-Water Pass (CP 1610), Gough Dam (GD 1622 and GD 1610), and London-Eye (LE 1601), within the Strangways Metamorphic Complex and crushed by selFragging. Subsequently, the zircon grains were imaged using Cathodoluminescence (CL) analysis and the U-Pb (uranium and lead) isotope ratios and the chrono-stratigraphy were measured. The imaged zircon revealed an anomalous heterogeneous crystal structure. Ellipses of the samples at locations GD1601, CP1610, and GD1622 fall below the intercept indicating the ages produced discordant patterns, whereas LE1601 intersects the Concordia curve at two points, implying the occurrence of an event of significant impact. For the rock sample at CP1610, the estimated mean age is 1742.2 ± 9.2 Ma with mean squared weighted deviation (MSWD) = 0.49 and probability of equivalence of 0.90; 1748 ± 15 Ma - MSWD = 1.02 and probability of equivalence of 0.40 for GD1622; and 1784.4 ± 9.1 Ma with MSWD of 1.09 and probability of equivalence of 0.37 for LE1601. But for samples at GD1601, two different age groups with different means occurred: 1) below the global mean (1792.2 ± 32 Ma) estimated at 1738.2 ± 14 Ma with MSWD of 0.109 and probability of equivalence of 0.95 and 2) above it with mean of 1838.22 ± 14 Ma, MSWD of 1.6 and probability of equivalence of 0.95. Analysis of the zircon grains has shown a discrepancy in the age range between 1700 Ma and 1800 Ma compared to the ASO dated to have occurred between 440 and 300 Ma. Moreover, apparent similarity in age of the core and rim means that the mineral crystallized relatively quickly without significant interruptions and effect on the isotopic system. This may have constraint the timing and extent of geological events that might have affected the mineral, such as metamorphism or hydrothermal alteration.

• Journal of the Korean Chemical Society
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• v.12 no.2
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• pp.51-54
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• 1968

Rapid flame spectrophotometric method is developed to determine a small amount of sodium in zircon frit and high purity zirconium compounds. The instrumental characteristics and the optimum conditions are studied and a comparison between calibration curve method and standard addition method is made.

• Proceedings of the KSEEG Conference
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• 2005.04a
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• pp.109-110
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• 2005

• Economic and Environmental Geology
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• v.28 no.6
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• pp.599-612
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• 1995

Some REE ore deposits are located in the middle part the of Korean peninsula. Geotectonically, the REE ore deposits situated on the Kyemyeongsan Formation of northern margin of the Okcheon geosynclinal belt and in the transitional zone between Kyeonggi massif and the Okcheon belt, with a deep-seated fracture separating the two tectonic units. The Kyemyeongsan Formation are different in lithology and metamorphic grade from the Gyeonggi massif and the Okcheon super group. The sequence of Kyemyeongsan Formation is dominantly composed of acidic metavolcanic and volcaniclastic rocks associated with alkaline igneous rocks which are related to volcano-plutonism. The REE ore deposits contain mainly Ce-La, Ta-Nb, Y, Y-Nd and Nd-Th group minerals. More than 15 RE and REE minerals have been found in the deposits, such as allanite, fergusonite, thorite bestnaesite, euxenite, polyclase, monazite, columbite, (Nb)-rutile, okanoganite, sphene, zircon, illmenite and some other unknown minerals. According to the characteristics of the mineral association, the REE ore deposits may be divided into 4 ore types; Zircon-REE, allanite-REE, feldspar-REE and fluorite-REE type. The Sm-Nd isochron age of the REE ore is 330 Ma, and the Sm-Nd model age is 1.11 Ga with ${\varepsilon}_{Nd(t)}$ being - 2.9. This data suggest that the REE ore deposit was formed in the early Carboniferous, and the ore-forming material came from the mantle. The REE ores show distinct light REE enrichment with strong negative Eu anomaly. The REE patterns of schistose rocks from Kyemyeongsan Formation are similar to felsic volcanics from rifts or back arc basins in or near continental crust. The genesis of the REE ore deposit is quite complicated. Different geologic processes are displayed in the studied area; sedimentation, volcanic activity, metamorphism and hydrothermal replacement. Alkali granite has suffered extensive post-magmatic metasomatism of a high temperature to produce alkali metasomatites. Geochemical charateristics show that metasomatism of alkaline fluid was probably the dominant ore-forming process in Chungju district.

• Journal of the Mineralogical Society of Korea
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• v.15 no.1
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• pp.11-21
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• 2002

A mineralogical study was made in order to identify the relationship between uranium content in groundwater and rock chemistry using core rocks recovered from the drilling holes for wells in the Daebo Granite areas. Uraniferous minerals are of primary origin and occur as inclusions in accessory minerals such as zircon, monazite, and xenotime. Since the uraniferous minerals are very small to be 1 ~ 2 $\mu$m in size, it is difficult to distinguish their mineralogical species precisely. The frequent presence of dissolution cavities or dissolved textures in the accessory minerals suggests that uraniferous minerals dissolved partially and contributed to the groundwater chemistry. Because there is no clear relationship between host rocks and groundwater for uranium concentration, mineralogical characteristics of uraniferous minerals, together with aqueous geochemical conditions favorable for uranium dissolution, could play important roles in groundwaster chemistry.