• 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.24 no.4
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• pp.363-378
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• 1991

Field and microscopic evidence, XRD,EPMA and chemical data suggest that parent rock of talc ore deposits of Yesan district was originated from ultramafic igneous rock. Parent rock can be divided into serpentinized dunite, serpentinized peridotite, metagabbro, amphibolite and hornblende schist. The ore deposits are highly sheared, and show many evidences of hydrothermal alteration and metamorphism at the greenschist and albite-epidote amphibolite facies. The process of steatitization is variable depending upon the composition, and the degree of alteration and metamorphism of the parent rocks. Steatitization can be divided into two processes with or without serpentinization. The parent rocks with serpentinization are serpentinized dunite, serpentinized peridotite and metagabbro, showing the following alteration process; olivine ${\rightarrow}$ serpentine${\rightarrow}$ talc. The rocks without serpentinization are amphibolite and hornblende schist showing the following sequence; hornblende${\rightarrow}$ chlorite${\rightarrow}$ talc. Formation of talc deposits is summarized as following six stages; I) Intrusion of ultramafic rocks, 2) autometamorphism, 3) metamorphism at greenschist and albite-epidote-amphibolite facies, 4) brittle deformation, 5) hydrothermal alteration, 6) purification of low-grade talc by late dyke intrusion.

• Economic and Environmental Geology
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• v.10 no.2
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• pp.67-74
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• 1977

Biggest talc deposits of South Korea, localized in Choong-Chung-Nam-do, are known as a products of hydrothermal metamorphism of serpentine. From studying mineral paragenesis and localization, three types of talc mineralization is presumed as follows: 1) Extended talc mineralization from autometamorphism (serpentinization) of ultra-basic igneous rocks, 2) Schistose talc rock as green schist facies of regional metamorphism and 3) Late hydrothermal mineralization and purification of serpentine and pre-existing low grade ores.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.344-344
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• 1999

• Journal of the Mineralogical Society of Korea
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• v.17 no.3
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• pp.221-233
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• 2004

Mineralogical characteristics and genesis of phlogopite in the talc deposits of the chungnam area were studied. Mica is one of the major impurity of talc ores in the study area. Talc-related micas show typical phlogopite composition, whereas talc-unrelated micas show wide compositional variations between biotite and phlogopite. Phlogopite mainly occurs in the black-wall type zone, especially in the nodular talc ores near the outer part of talc ore bodies. Interleaving textures of phlogopite and chlorite are easily observed under the optical microscope and back-scattered electron images. Interleaving textures of phlogopite and talc are observed also. Examination of the phlogopite by transmission electron microscope reveals that 14 $\AA$ layers of chlorite are randomly interlayered within the 10 $\AA$ layers of phlogopite, which suggests that the genesis of phlogopite is closely related to chlorite. Considering the occurrence and mineralogical characteristics of phlogopite, and the possible origin of K for the formation of phlogopite, phlogopite of the study area was formed by interaction between talc ore body and hydrothermal solution containing sufficient K at the late stage of talc formation. K might be introduced from the granitic gneiss at the contact zone between the talc ore body and the granitic gneiss under favorable structural condition for the potash metasomatism.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.95-103
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• 1993

The geology of the talc ore deposits in the Chungju area consists of the Kyemyeongsan Formation, the Munjuri Formation, the Daehyangsan Quartzite, the Hyangsanni Dolomite, and the basic rocks of the Ogcheon belt. The talc ore occurs in the Hyangsanni Dolomite near the Daehyangsan Quartzite The mineral assemblages in the Hyangsanni Dolomite are \circled1calcite-tremolite-talc-quartz, \circled2calcite-talc-quartz, \circled3tremolite-calcite-dolomite, and \circled4calcite-dolomite-phlogopite-chlorite. Talc has almost the ideal composition($X_{Mg}$=Mg/(Fe+Mg)=0.98). Talc was formed in siliceous dolomite by the medium-pressure type regional metamorphism. The evidences for contact metamorphism and/or hydrothermal reaction are not clear. The metamorphic grade of the Hyangsanni Dolomite and its adjacent pelitic or basic rocks near the deposits corresponds to epidote-amphibolite facies or greenschist facies based on the, mineral assemblages of \circled1hornblendebiotite-muscovite-epidote-quartz \circled2biotite-chlorite-quartz, and \circled3hornblende-actinolite-plagioclasequartz. The formation of the talc deposits were caused by the following reactions due to greenschist facies metamorphism of siliceous-dolomitic rocks in the Hyansanni Dolomite. (I) 3 dolomite+4 quartz+$H_2O$= talc+ 3 calcite +3 $CO_2$; (11) 3 tremolite+ 2 $H_2O$+ 6 $CO_2$= 5 talc+ 6 calcite + 4 quartz. The minimum temperature of the talc-tremolite-quartz assemblage is about $434^{\circ}C$ from calcite thermometry and the carbon dioxide mole fraction in metamorphic fulid($X_{$CO_2$}$) is about 0.1 at assumed pressure, 3 kbar.

• Proceedings of the KSEEG Conference
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• 2005.04a
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• pp.275-278
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• 2005

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.195-204
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• 2005

Interlayered structures of talc and chlorite in the talc deposits of the Yugu area are studied using transmission electron microscope. Packets of chlorite-like layer in talcs or packets of talc-like layer in chlorites are commonly observed. Randomly interlayered features of talc and chlorite are locally observed in some specimens. Reactions observed in the present study include the addition or removal of a brucite-like layer in the interlayer region of the talc or chlorite resulting in the , transformation between a talc and a chlorite layers and breakdown or formation of a talc-like layer resulting in transformation between two talc layer and one chlorite layer. Both reactions are accompanied by a significant change in volume. In addition to these mechanisms, there are two volume conserving mechanisms; the combination of both mechanisms and mutual transformation in a complex manner. Reactions from 2 chlorite layers to 3 talc layers, from 2 chlorite layers + 1 talc layers to 1 chlorite layers + 3 talc layers, and from 3 chlorite layers to 5 talc layers are observed among the complex type mechanisms.

• The Journal of the Petrological Society of Korea
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• v.3 no.2
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• pp.156-170
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• 1994

The talc ore deposits can be divided into chloritic and dolomitic ores according to mineral assemblages. The former is mainly composed of chlorite and talc accompanied with dolomite, muscovite and opaque mineral, and the latter of dolomite and talc with serpentine, calcite and magnesite in places. Talc was originated from chlorite and serpentine. Carbonate minerals were formed either directly from the introduced hydrothermal solution or secondarily as a by-product of steatitization of chlorite and serpentine. The process of talc formation may be governed by the chemical composition of the host rocks and the amount and/or chemical composition of the hydrothermal solution which may be different in places. However, the representative reactions producing talc from chlorite and serpentine are as follows : (1) chlorite+$Mg^{++}+Si^{4+}+H_2O$=talc, (2) chlorite+$Mg^{++}+Si^{4+}+Ca^{++}+CO_2+O_2+H_2O$=talc+ dolomite+ magnesite, and (3) serpentine +$Mg^{++}+Fe^{++}+Si^{4+}+Ca^{++}+CO_2+H_2O$=talc+dolomite. The reactions indicate that the carbonate minerals can be formed when the hydrothermal solution have high $fO_2$ and $fCO_2$. The steatitization might be proceeded by the hydrothermally metasomatic reaction between chlorite schist or chlorite gneiss intercalated in the granitic gneiss and hydrothermal solution accompanied to the wet granitization.

• Journal of the Mineralogical Society of Korea
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• v.17 no.4
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• pp.357-364
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• 2004

Mineral chemistry of talc from the Dongyang talc deposits was studied to characterize the differences between dolomite-origin talc (talc I) and tremolite-origin talc (talc II). Average iron and aluminum contents are higher in talc II, 2.18 wt% FeO and 0.31 wt% $Al_2$O$_3$), than in talc I, 1.48 wt% FeO and 0.08 wt% $Al_2$O$_3$). Consistently lower Mg/(Mg+Fe+Mn) ratios and higher AI concentrations with uniform values of talc II compared to talc I seem to reflect the compositional differences of the original materials, tremolite and dolomite, respectively. Relative enrichment of Al as well as Fe in talc II compared to tremolite can be attributed to their immobile behaviors during alteration process and the rapid diffusion of hydrothermal fluids, which can accelerate instantaneous nucleation with immaturity growth of talc II. Increase in the concentrations of talc II can lower the ore grade by increasing concentrations of impure components such as AI and Fe, and by abundant presence of tremolite as well.