• Economic and Environmental Geology
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• v.30 no.5
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• pp.477-491
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• 1997

In the Bibong area of the western part of Chungcheongnam-do, ultramafic masses occur as discontinuous isolated lenticular bodies in the Precambrian Kyeonggi gneiss complex. They extend for about 200 m long to NNE directions which are parallel to fault lines in the gneiss complex. The ultramafic masses contact with the adjacent gneiss complex as steeply dipping faults. They are dunites and harzburgites and many of them are partially or completely serpentinized. The ultramafic rocks dominantly show protogranular, equigranular and equigranular-$m{\grave{o}}saic$ textures. They also show porphyroclastic (megacrystic) or recrystallized textures reflecting several stages of metamorphism. They contain varying amounts of olivine $(Fo_{89-92})$, enstatitic to bronzitic orthopyroxene, diopsidic clinopyroxene, tremolitic to pargasitic hornblende, and spinel with serpentine, talc, chlorite, calcite and magnetite. The ultramafic rocks have high magnesium numbers and transitional element contents, low alkali contents and show deplete REE patterns. Comparing with available data, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to those of worldwide mantle xenoliths and orogenic related ultramafic rocks. The field evidences, petrographical, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to alpine type ultramafic rocks emplaced into the crust by the faulting as mantle slab types. With the petrographical characteristics, these mineralogical compositions suggest that the ultramafic rocks of the Bibong area have experienced several stages of retrogressive metamorphism in a condition ranging from the upper amphibolite facies to greenschist facies.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.196-197
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• 2003

Several masses of the alpine type ultramafic rocks are found within the Precambrian Kyeonggi gneiss complex, western part of Chungnam province. They occur as discontinuous isolated lenticular bodies along the fault line(NNE direction), dominant tectonic directions of Kyeonggi gneiss complex. The ultramafic rocks occur as fault contacts with the adjacent Precambrian metamorphic and metasedimentary rocks. (omitted)

• Economic and Environmental Geology
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• v.37 no.5
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• pp.477-497
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• 2004

In the Hongseong and Kwangcheon areas, two ultramafic rocks are exposed as isolated bodies in the Precambrian Kyeonggi gneiss complex. The ultramafic rocks extend for several hundred meters to NNE direction and are contact with adjacent metasediments by steeply dipping faults. The rocks are dunite or harzburgite showing dominantly equigranular-mosaic and protogranular textures with a minor amount of porphyroclastic textures. They contain varying amounts of fosteritic olivine (F$o_{0.91-0.93}$), magnesian pyroxene (E$n_{0.89-0.93}$) and tremolitic to magnesian hornblende with minor amounts of spinel, serpentine, chlorite, magnetite, phlogopite and talc. The rocks are in contrast with adjacent gneiss complex or metabasite (amphibole, biotite, plagioclase, alkali-feldspar and quartz). Geochemically, these ultramafic rocks are characterized by high magnesium number (M$g_#$> 0.88) and transitional element (mainly, Ni>1716 ppm, Cr>1789 ppm), low alkali element (e.g. $K_2$O<0.09 wt.%, Na$_2$O<0.19 wt.%) and depletion of incompatible elements. The calculated correlation coefficients showed good positive correlations among the ferrous (e.g. Sc, V, Zn) elements, incompatible elements (e.g. REE), and among SiO$_2$ or $Al_2$O$_3$ with ferrous elements, whereas negative correlations are appeared between Ni and major elements. These results involve increasing of the ferrous- and $Al_2$O$_3$-bearing minerals(e.g. amphibole and mica) with decreasing of Mg-bearing minerals (e.g. olivine) depending on the degree of alteration. Calculated geothermometries and mineral assemblages suggest that the ultramafic rocks have been metamorphosed through the condition from the greenschist to amphibolite facies. Compared with ultramafic rocks elsewhere, it is thought that those of the Hongseong and Kwangcheon areas are derivatives of the depleted sources since they are depleted in incompatible elements including REE abundances. Moreover overall characteristics of the ultramafic rocks are similar to the those of orogenic related Alpine type ultramafic rocks, especially, shallow mantle slab varieties.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.26 no.3
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• pp.253-266
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• 2016

Objectives: This study is for characteristics of asbestos occurrence (NOA, naturally occurring asbestos) from the Gapyeong area and its host rocks, serpentinites. Methods: Representative samples are collected from the serpentinite bodies, following degrees of hydrothermal alteration and metamorphism, after about 2 year field trips. Mineralogical, morphological and optical characteristics of the asbestos and host rocks are confirmed by PLM, XRD EPMA and SEM results. Results: The serpentinites are dunites and harzburgites, and host asbestos, including chrysotile, tremolite and actinolite. The asbestos chrysotiles are found as veins ranging from several millimeters to several centimeters in thickness, while asbestos-tremolite and -actinolite occur along cracks and fractures ranging up to ten centimeters in thickness. The chryostiles occur mainly as cross and slip fibers, while the amphibole asbestos is found as vein, slip and oblique fibers. More tremolitic grains are colorless and commonly show elongated or fiber shapes, whereas the magnesio hornblende grains mainly show light green and occur as subhedral to euhedral diamond grains. Conclusions: Overall characteristics of serpentinites from the Gapyeong area are similar to worldwide orogenic-related Alpine type ultramafic rocks serpentinized and serpentinites in South Chungcheong-do Province, Korea, and occurrences of asbestos are similar to those of the ultramafic bodies in South Chungcheong-do Province.

• 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 Mineralogical Society of Korea
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• v.32 no.1
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• pp.15-39
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• 2019

An ultramafic complex occurs as an isolated lenticular body in the Andong area. The Andong ultramafic complex comprises ultramafic and mafic rocks, but mainly peridotites. The complex extends for several kilometer to ENE direction, adjacent to the Andong fault line. This study is for petrochemistry of the peridotites within the ultramafic complex and characteristics of asbestos occurrences. The peridotites are igneous origin, ranging from lherzolite to wehrlites and are characterized by high Fo olivine ($Fo_{0.85-0.87}$), Mg clinopyroxene ($Mg_{87.5-93.5}$), and tremolitic to tschermakitic hornblende. Geochemically, these rocks show high magnesium number (mainly Mg = 85.3-87.38) and transitional element and low alkali element contents. The peridotites host asbestos, including chrysotile, tremolite and actinolite asbestos, but dominated by amphibole asbestos. The amphibole asbestos are found along small fault face, and cleavage and fracture showing several cm to ten cm in width as slip and oblique fibers, while the chryostiles occur at cleavage and vein showing several mm-cm in width as cross and slip fibers. They are confirmed by PLM, XRD and SEM results. Overall characteristics of peridotites from the Andong ultramafic complex and occurrences of the asbestos are similar to those of worldwide orogenic related Alpine type ultramafic rocks and serpentinized ultramafic bodies in Chungnam, Korea, respectively.

• Journal of the Korean earth science society
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• v.21 no.3
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• pp.323-336
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• 2000

Ultramafic rocks in Choongnam area are mainly serpenitinites which are parent rock of talc and asbestos ore deposits. About 10 $^{\circ}$ NNE-trending parallel serpentinites masses occur as discontineous isolated lenticular intrusive bodies in Precambrian gneiss complex between Hongseong-Kwangcheon line and Onyang-Cheongyang line. The sizes of serpentinites vary from several centimeters to 1 kilometer in width and from several meters to 5 kilometers in length. The serpentinites show high SiO$_2$(39.99wt.% in average), MgO(38.46wt % in average), Cr(>1011ppm), Ni(>1660ppm), and Co(>80ppm). Most serpentinites contain serpentine more than 50%. Some serpentines contain original minerals such as olivine, pyroxene and chromite. Also, serpentinites body may contain a little serpentinized peridotite, and some talc and asbestos ore deposits. The original rocks of the serpentinites interpreted as Alpine type ultramafic rocks, and dunite and/or harzburgite which were originated from slightly depleted upper mantle(30${\sim}$40km deep), and emplaced in the crust through the large fault zones. It seems that main serpentinization from the original rocks was occurred during greenschist and/or amphibolite facies regional metamorphism in Choongnam area.