• Korean Journal of Mineralogy and Petrology
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• v.36 no.4
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• pp.323-336
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• 2023

We investigated the nickel potential and genesis of ultramafic rocks in the Yugu area to secure nickel resources in South Korea. The Yugu ultramafic rocks, located in the southwest of the Gyeonggi Massif, are characterized by spinel peridotite and exhibit strong serpentinization along their boundaries. The serpentinization is observed as olivine transformed to antigorite and chrysotile, while pentlandite, the nickel sulfide mineral, altered into millerite and awaruite. Serpentine displays distinct foliation, aligning subparallel to the ultramafic rock boundaries and foliation of Yugu gneiss. This suggests that the uplift of ultramafic rocks resulted in hydrothermal infiltration likely sourced from the Yugu gneiss metamorphism. The Yugu ultramafic rocks are residues after 5~18% partial melting of abyssal peridotite. Enriched light rare earth elements and Eu imply secondary metasomatism. Geochemistry suggests a link between the formation of Yugu ultramafic rock and the Triassic collision of the North and South China continents. The nickel content is around 0.17~0.21%, mainly contained in olivine and serpentine. Hence, in addition to the mineral processing study on the sulfide minerals, focused studies on oxide minerals for enhanced nickel recovery within the Yugu ultramafic rock are strongly suggested.

• Economic and Environmental Geology
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• v.27 no.2
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• pp.131-145
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• 1994

The Daehung and Pyeongan talc mines are located in the Yoogoo area, Chungcheongnam-Do. These deposits occur as the complex vein type in the ultramafic rocks which intruded Precambrian gneiss. The talc ore formed from sepentinitt: originated from ultramafic rocks but some of those from hornblende gneiss. The talcification processes were considered here on the basis of the mineral assemblages, paragenesis, and geochemistry. It appears that there are five processes in talcification ; serpentine$\rightarrow$talc, phlogopite$\rightarrow$chlorite$\rightarrow$talc, phlogopite$\rightarrow$talc, hornblende$\rightarrow$chlorite$\rightarrow$talc, and hornblende$\rightarrow$talc. Among them, the most dominant alteration path is serpentine to talc in these deposits. EPMA data suggest that there might be interstratified minerals were in between parent mineral and talc such as serpentine and talc, and phlogopite and talc. It can be found that tremolite exists in between the inner and outer most part of talcified serpentinite blocks coated with phlogopite. Some of tremolites has been altered to talc. The quartz veins and carbonate minerals were found in the talc ore zone. It indicates that the hydrothermal solution played an important role in talcification. The hydrothermal alteration occured after sepentinization. Ore zones can be divided into two zones; talc-serpentine zone preserving a pseudormorph of olivine (mesh texture) and talc-phlogopite zone showing talcification from phlogopite directly or through chlorite. It can be concluded that the formation of major talc ore body was due to talcification of serpentinite and phlogopite by hydrothermal solution. A nature of hydrothermal solution was relatively pure water at the beginning of serpentinization, and was getting richer in silica composition. There was a large amount influx of K and AI with hydrothermal solution in the later stage, and increased $P_{CO_{2}}$ also. It suggests that phlogopite formed in later stages as a secondary mineral. So, the major part of the talc ore body was formed from one parents rocks, serpentinite originated from ultramafic rocks, by hydrothermal solutions at several times.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.29-40
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• 1993

Several vermiculite deposits occur as the alteration product from phlogopite in ultramafic rock, in the Hongseong and Cheongyang area, South Korea. Some quarries show well-defined weathering profile. Samples collected from those quarries were examined by XRD and chemistry to define a vertical variations in mineralogy and chemistry of the weathering profile developed on ultramafic rocks. The analysis by X-ray diffractometry showed that mineral compositions changed continuously as depth of profile increasing, the vermiculite-the phlogopite/vermiculite interstratified-the phlogopite. Chemical analysis of bulk samples in altered zone revealed that regardless of composition and kinds of mineral in the rock, there are significant increase of MgO, CaO and $H_2O$, and decrease of K as depth of profile decrease reflecting the characteristics in vermiculitization. Also, there was a tendency that weathering indicies of each sample horizon change gradually with increasing depth. This tendency can be explained as variations of degree of vermiculitization. The regular changes of mineralogical and chemical composition in vertical profile suggest that weathering is the most important process in vermiculitization in this area.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.447-458
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• 1998

The spinel Ihelzolite of ultramafic xenoliths are found in the alkali basalt from eastern part of the Cheju island, Korea. The xenolith is are mainly composed of olivine, orthopyroxene, clinopyroxene and spinel. Based on the chemical compositions of the constituent minerals, the ultramafic xenolith belong to upper mantle peridotite. Each minerals have a protogranular texture. Olivine with kink band texture partly shows undulatory extinction. Some clinopyroxenes have spongy textured rims. Brown spinels occur in the interstices between olivine and pyroxene grains. Olivine is mostly forsterite $(Fo_{89-90})$. Orthopyroxene is enstatite $(Wo_{1.3}En_{88.4}Fs_{10.3})$ with 3.87~5.25 wt% $Al_{2}O_{3}$. Clinopyroxene is diopside $(Wo_{48.0}En_{46.2}Fs_{5.8})$ with 6.75~5.03 wt% $Al_{2}O_{3}$. Spinel has the Mg value of 75.9 and its Cr-number is 10.2. According to the PoT estimations for the mantle xenoliths, equilibrium temperatures of the xenoliths range from 1023 to $1038^{\circ}C$ and pressure is 18 kbar. Spinellhelzolite from this area, which is characterized by lower Cr-number (10.2) and homogeneous chemical compositions, supports that these ultramafic xenoliths are derived from the upper mantle.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.261-270
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• 2019

Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the $45^{\circ}$ line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

• The Journal of the Petrological Society of Korea
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• v.12 no.4
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• pp.170-183
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• 2003

The Sokli complex in the northeastern Baltic Shield (Finland) forms a part of the extensive Devonian Kola Alkaline Province. The complex contains ultramafic lamprophyres occurring as dikes of millimetric to metric thickness. The Sokli ultramafic lamprophyres have petrographical and geochemical affinities with aillikite. High concentrations of Cr and Ni with low Al$_2$O$_3$ content of the Sokli aillikites indicate a strongly depleted harzburgitic source. However, compared to the kimberlites, the lower Cr and Ni contents and mg-number with weaker HREE depletion of the Sokli aillilkites imply a smaller proportion of garnet in the source and thus suggest a shallower melting depth of the source. In order to account for high concentrations of all incompatible elements and LREEs, with high volatile content (especially CO$_2$), an additional enriched material is thought to have been incorporated into the Sokli aillikite source. An anomalous enrichment of K in the Sokli aillikites, compared to nearby ultrapotassic rocks and world-wide ultramafic lamprophyres, indicate a presence of K-rich phase (probably phlogopite) in the source mantle.

• Journal of Conservation Science
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• v.35 no.2
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• pp.131-144
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• 2019

The Seosan Geomenyeo(black submerged rocks), once located at the Cheonsuman bay of Buseokmyeon in Seosan, Korea, is a reef rock now exposed on the land surface. The Geomenyeo can also be found in the ancient geographic maps around the area. The local geographic names, like Buseok and Buseoksa temple are derived from the Geomenyeo. It is composed of ultramafic rocks complex and intrusive felsic igneous rocks. These rocks show diverse facies with various petrographic characteristics caused by geological processes such as intrusion and alteration. Ultramafic rocks complex can be roughly categorized as coarse grained ultramafic rocks and medium grained mafic rocks. Both cases are composed of pyroxene and amphibole, showing the general rock facies of pyroxenite, diabase and lamprophyre. Felsic igneous rocks includes pinkish medium grained granite, porphyritic amphibole granite and aplite with varied mineral compositions. The Geomenyeo is the only ultramafic rocks complex in the Cheonsuman Bay; moreover, it has a distinctive geological and scenic value, as well as a symbolic property. In order to preserve the Geomenyeo, it is necessary to investigate and promote it as a designated heritage site through academic studies, and compensate for the convenience and protection facilities. Additionally, the Geomenyeo should be evaluated as a maritime heritage site, due to the unique local culture as it succeeds the recognition of forefathers which regarded it as a local scenic site with significance.

• Economic and Environmental Geology
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• v.34 no.4
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• pp.395-415
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• 2001

In the Singok area, western part of Chungcheongnam-Do, two ultramafic ma~ses, Singok mass and Kaewol mass, occur as isolated lenticular bodies in the Precambrian Kyeonggi gneiss complex. The masses extend for several hundred meter to NNE direction, parallel to the main fault line of this area. The rocks are dunite and harzburgite, but partially and absolutely serpentinized. They dominantly show porphyroclastic and recrystallized textures with equigranular-mosaic and protogranular textures. In spite of differences among the alteration and metamorphism, the ultramafic masses are characterized by varying amounts of high fosteritic olivine ($Fo_{0.88-0.93}$), magnesian pyroxene ($En_{0.93-0.97}$), and tremolitic to tschermakitic hornblende with minor spinel, serpentine, chlorite, calcite, magnetite, phlogopite and talc. It is compared with adjacent gneiss complex containing amphibole, biotite, plagioclase, alkali-feldspar and quartz. Geochemically, these rocks show high magnesium number (Mg>90.38), and transitional element (Ni=595-2480, Cr==IOlO-4400, Co=36-120 ppm), low alkali element ($Na_{2}O$<0.3, $K_{2}O$<0.11, $Al_{2}O_3$<2.95 wt%) and depleted incompatible element contents, which is compared with adjacent rocks (Mg < 83.69, $Na_{2}O$=1.02-3.42 wt%, $K_{2}O$=O.67-5.65 wt%, $Al_{2}O_3$=9.15-16.86 wt%, Ni < 435 ppm, Cr < 1440 ppm, Co<59 ppm, enriched incompatible element contents). Overall characteristics of ultramafic rocks from the Singok and Kaewol masses are similar to the those of adjacent ultramafic bodies in Chungnam with worldwide orogenic related Alpine type ultramalic rocks. Calculated geothermometries suggest that the ultramafic rocks have experienced metamorphism in the condition ranging from the greenschist facies to granulite facies.

• Journal of the Korean earth science society
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• v.44 no.4
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• pp.307-317
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• 2023

We investigate the provenance of detrital garnets in Middle-Upper Jurassic sandstone of the Mino terrane, an accretionary complex in Southwest Japan, based on their chemical composition. The garnet grains in the Mino sandstone are mostly Fe-rich (almandine) and slightly Mg-rich (pyrope) species derived from high-grade metamorphic and intermediate to acidic plutonic rocks. The composition and interpreted origin of the garnets are generally consistent with those of metamorphic and igneous rocks of the Yeongnam Massif on the Korean Peninsula, a possible source region suggested in previous studies. In addition, two single grains of chromian spinel, an accessory mineral found in mafic to ultramafic rocks such as mantle peridotite, were found in one of the Mino sandstone samples. This finding suggests the possible presence of mafic to ultramafic rocks in the source area. The results of this study provide complimentary evidence for establishing a comprehensive tectonic and paleogeographical framework for the Mesozoic East Asian continent.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.167-167
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• 1999