• Journal of the Mineralogical Society of Korea
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• v.23 no.1
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• pp.73-84
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• 2010

We studied the geological occurrence, associated minerals, mineralogical properties and formation process of tremolites from two abandoned asbestos mines, Jungang (Sinsuk) and Daebosuksan, located in Boryoung area, Chungnam. Morphologically different tremolites such as long fibrous, needle-like, bladed and prismatic forms coexisted. Fibrous tremolite, known for its high toxieity to human health, was systematically analyzed by polarized light microscopy and scanning electron microscopy. The average length of tremolite fibers was 31.2 ${\mu}m$ although the maximum length of some asbestos was 210.0 ${\mu}m$. The average width and aspect ratio were 1.6 ${\mu}m$ and 19.9, respectively. Tremolite showed inclined extinction in the range of 6.1~20.2$^{\cric}$. X-ray diffraction patterns were slightly different between fibrous (asbestiform) and prismatic (non-asbestiform) tremolites. EPMA analysis of tremolites in the study area indicated extremely high Mg content with very low Fe content, close to the composition of tremolite in end-member in the tremolite-actinolite solid solution series. The formational conditions of asbestiform and non-asbestiform tremolite appear to be different. Asbestiform tremolite was estimated to have been formed in later stage.

• The Journal of the Petrological Society of Korea
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• v.1 no.2
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• pp.104-123
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• 1992

We present petrography, mineral chemistry of amphibole and plagioclase, and major and trace element chemistry for the Ogcheon metabasites occurring in the Poun and Mungyong areas to understand metamorphism, and to define chemical characteristics of parental rocks and their implication for tectonic environment. The Ogcheon metabasites often preserve relict igneous textures, although no primary phases are observed. They are mainly composed of amphibole (actinolite+hornblende)+plagioclase+epidote+chlorite+sphene+opaque oxides, indicating epidote amphibolite facies metamorphism. Coarse-grained amphiboles frequently have actinolitic composition in the core, and hornblende along the margin and cleavage, which can be interpreted either as miscibility gap or as result of polymetamorphism. Although presumed polymetamorphic events in the Ogcheon supergroup favor the latter possibility, further metamorphic studies are necessary to solve the problem. Amphibole and plagioclase chemistries suggest greenschist (epidote-amphibolite, if miscibility gap is present) to amphibolite facies metamorphism of possibly medium pressure. The major and trace element data of whole rocks indicate that the Ogcheon metabasites are transitional to tholeiitic basalts belonging to within-plate environment. Absence of evidences indicating deep sea environment suggests that the Ogcheon metabasites emplaced in an intra-cratonic, possibly rift environment which failed to proceed to an oceanic rift. Chemical variation of the metabasites toward a granitic pluton indicates K loss closer to the pluton, suggesting that caution should be taken when K is involved in a discussion.

• The Journal of the Petrological Society of Korea
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• v.1 no.1
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• pp.1-24
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• 1992

Precambrian metamorphic rocks of the Gapyeong-Cheongpyeong area consist of banded gneiss, augen gneiss, leucocratic gneiss, quartz schist and quartzite, together with minor intercalations of serpentinite, amphibolite and marble. Mineral assemblages of meta-sedimentary rocks are classified into three types: sillimanite-free; sillimanite-bearing; and sillimanite+K-feldspar-bearing assemblages. Compositions of metamorphic phases depend on the type of mineral assemblages. In particular, the Ca contents of plagioclase and garnet are high in sillimanite-free assemblges. Kyanite occurs in three samples, and coexists with sillimanite in one sample. The presence of kyanite indicates that metamorphic rocks of the study area have experienced the Barrovian type metamorphism. Peak metamorphic conditions estimated from various geothermobarometers and phase equilibria are 618-674$^{\circ}C$ and 6.5${\pm}$2.0 kbar for sillimanite-free assemblages, and 701-740$^{\circ}C$ and 4.4${\pm}$0.8 kbar for sillimanite-bearing assemblages, respectively. Furthermore, a clockwise P-T-time path is deduced for the study area, based on the following observations: (1) the polymorphic transition of kyanite to sillimanite, (2) the occurrence of sillimanite and K-feldspar belonging to the upper amphibolite facies, and finally (3) the retrograde metamorphism characterized by muscovite-, chlorite-, and actinolite-bearing assemblages.

• 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.

• Korean Journal of Mineralogy and Petrology
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• v.34 no.2
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• pp.107-120
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• 2021

The Komdok Pb-Zn deposit, which is the largest Pb-Zn deposit in Korea, is located at the Hyesan-Riwon metallogenic zone in Jiao Liao Ji belt included Paleoproterozoic Macheolryeong group. The geology of this deposit consists of Paleoproterozoic metasedimentary rocks, Jurassic Mantapsan intrusive rocks and Cenozoic basalt. The Komdok deposit which is a SEDEX type deposit occurs as layer ore and vein ore in the Paleoproterozoic metasedimentary rocks. Based on mineral petrography and paragenesis, dolomites from this deposit are classified four types (1. dolomite (D₀) as hostrock, 2. early dolomite (D₁) associated with tremolite, actinolite, diopside, sphalerite and galena from amphibolite facies, 3. late dolomite (D₂) associated with talc, calcite, quartz, sphalerite and galena from amphibolite facies, 4. dolomite (D₃) associated with white mica, chlorite, sphalerite and galena from quartz vein). The structural formulars of dolomites are determined to be Ca_1.00-1.20Mg_0.80-0.99Fe_0.00-0.01Zn_0.00-0.02(CO₃)₂(D₀), Ca_1.00-1.02M_0.97-0.99Fe_0.00-0.01Zn_0.00-0.02(CO₃)₂(D₁), Ca_0.99-1.03Mg_0.93-0.98Fe_0.01-0.05Mn_0.00-0.01As_0.00-0.01(CO₃)₂(D₂) and Ca_0.95-1.04Mg_0.59-0.68Fe_0.30-0.36Mn_0.00-0.01 (CO₃)₂(D₃), respectively. It means that dolomites from Komdok deposit have higher content of trace elements (FeO, MnO, HfO₂, ZnO, PbO, Sb₂O₅ and As₂O₅) compared to the theoretical composition of dolomite. These trace elements (FeO, MnO, ZnO, Sb₂O₅ and As₂O₅) show increase and decrease trend according to paragenetic sequence, but HfO₂ and PbO elements no show increase and decrease trend according to paragenetic sequence. Dolomites correspond to Ferroan dolomite (D₀, D₁ and D₂), and Ferroan dolomite and ankerite (D₃), respectively. Therefore, 1) dolomite (D₀) as hostrock was formed by subsequent diagenesis after sedimentation of Paleoproterozoic (2012~1700 Ma) silica-bearing dolomite in the marine evaporative environment. 2) Early dolomite (D₁) was formed by hydrothermal metasomatism origined metamorphism (amphibolite facies) associated with intrusion (1890~1680 Ma) of Paleoproterozoic Riwon complex. 3) Late dolomte (D₂) was formed from residual fluid by a decrease of temperature and pressure. and dolomite (D₃) in quartz vein was formed by intrusion (213~181 Ma) of Jurassic Mantapsan intrusive rocks.