• Economic and Environmental Geology
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• v.38 no.4 s.173
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• pp.421-434
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• 2005

Abstract Based onthe characteristics of Carlin-type gold deposit in Nevada district, a potential in Korea is evaluated to the Yemi area where is structurally controlled by folds and trust fault. The fault of high angles are combined with a more permeable rocks such as the Yemi breccia and laminated silty limestone. The pattern of enrichment factors for Tl, Sb, As, Ag, Pb, Zn, Cu, Mo and W of limestones in the southern area are geochemically similar with those reported from the Carlin-type Bold deposit. Moreover, the oxygen and carbon isotopes show a hydrothermal alteration is widely developed in this area. According to the result of geophysical interpretation, stable isotope, alteration mineralogy, geochemical study, and geological structure, this mineralized zone may be extended to the M direction, so a detailed systematic exploration is required to identify this alteration zone.

• Journal of the Mineralogical Society of Korea
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• v.7 no.1
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• pp.25-39
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• 1994

The Deogbong napseok clay deposit which is composed mainly of dickite and pyrophyllite has been formed by hydrothermal alteration of the Late Cretaceous volcanic rocks consisting of andesitic tuff and andesite. The mineralogy of the napseok ores and the hydrothermal alteration processes have been studied in order to know the nature of the interaction between minerals and fluids for the formation of the deposit. Chemical distribution shows that alkali elements and silica were mobile but alumina was relatively immobile during the hydrothermal processes. It is evident that enrichment of alumina and leaching of silica from the host rock led to the formation of the napseok ore, whereas the enrichment of silica in the outer zone of the deposit gave rise to the silica zone. A large amount of microcrystalline quartz closely associated with dickite and pyrophyllite suggests the increasing activity of silica. Thus Si which was released away from the argillic zone by the increasing activity of silica. Thus Si which was released away from the argillic zone by the increasing activity of silica solubility moved out precipitating in the margin of the deposit to form the silica zone. Variation in dickite crystallinity implies the local change in the stability of the system. Thermodynamic calculation shows that the invariant point of pyrophyllite-dickite (kaolinite)-diaspore-quartz assemblages at 500 bars in the system $Al_{2}O_{3}-SiO_{2}-H_{2}O$ is about 300 $^{\circ}C$. Based on the mineral assemblages and the experimental data reported, it is estimated that the main episode of hydrothermal alteration occurred at least above 270 to 300 $^{\circ}C$ and $X_{CO_2}$ <0.025. Mineral occurrence and chemical variation indicate that the activity of Al is high in the upper part of the deposit, whereas the activity of Si is high in the lower part and the margin of the deposit. The nonequilibrium phase relations observed in the Deogbong deposit might be due to local change in intensive thermodynamic variables and fluid transport properties that resulted in the formation of nonequilibrium phases b of several stages.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.169-181
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• 2014

Korea government has consistently investigated the development of economic mineral deposits in the Tofua volcanic arc, Tonga since 2008 for the secure of sea floor mineral resources. We studied the composition and distribution of minerals formed by hydrothermal activity around TA 25 seamounts of the Tofua volcanic arc, Lau Basin, Tonga, using X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence spectrometry, and inductively coupled plasma atomic emission spectrometry. We used 7 core samples and 9 surface sediment samples. Barite, sphalerite, and clinoclase are present in the most volcanic vent area. Gypsum, smectite, and kaolin mineral are distributed in vent A area, chalcopyrite, pyrite, smectite, and kaolin mineral are in vent B and C area, and gypsum, chalcopyrite, pyrite, and goethite are in vent D area. From the study of clay fraction, smectite and few kaolinite are detected in the most studied area except inner part of caldera, which suggest that argillic alteration are dominant in the volcanic vent areas. Various sulfide or arsenide minerals were found in the hydrothermal vent B, C, and D. The mineralogy and geochemistry suggest higher hydrothermal activities in volcanic vent B, C, and D compared to vent A and inner caldera area. Therefore higher probabilities of massive sulfide deposits may occur in hydrothermal vent B, C, and D.

• Economic and Environmental Geology
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• v.21 no.1
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• pp.57-67
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• 1988

K-Ar age determinations were carried out on muscovite and other gangue and wallrock alteration minerals from seventeen mineral deposits in the Taebaeg mountain district. Tin deposits give the ages of 1792 Ma and 158-127 Ma, whereas tungsten-molybdenum deposits give the ages of 1520-1480 Ma. 173-168 Ma and 84-81 Ma. Polymetallic mineral deposits. gold-silver deposits and sericite deposits yield the ages of 98-52 Ma. 93-75 Ma, and 202 Ma, respectively. Mineralization ages for each genetic type of deposits in this district can be summarized as follows; pegmatite deposits. 1792 Ma ; pegmatite-hydrothermal deposits. 1526-1480 Ma ; greisen deposits. 157-127 Ma ; skarn deposits, 98-73 Ma and 52 Ma ; hydrothermal deposits, 202-168 Ma and 93-76 Ma. Present results together with data available in the literature reveal that five distinct mineralization ages can be recognized in this district ; (1) 1792 Ma, (2) 1526-1480 Ma, (3) 202-127 Ma. (4) 98-73 Ma, (5) 52 Ma, These age data are similar to the reported radiometric age data of igneous rocks in this district except for two ages such as 2154-2084 Ma and 880-738 Ma.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.375-388
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• 1998

The purpose of this study is to investigate the ore genesis and occurrence of the Wondong polymetallic mineral deposits. The Pb-Zn, Fe and W-Mo mineralizations are found in skarn zones which formed mainly in or along the fault shear zones with the $N25-40^{\circ}W$ and $N10-50^{\circ}E$ directions, whereas the Cu-Mo mineralization is appeared hydrothermal replacement zone. The skarn minerals consist mainly of garnet and epidote, which were the last alteration phases between pneumatolytic and hydrothermal stages. The mineral paragenesis toward the late stage are as follows: arsenopyrite, scheelite, magnetite, pyrite, pyrrhotite, sphalerite, galena, chalcopyrite and molybdenite. Average ore grades are 0.33 g/t Au, 46.29 g/t Ag, 0.06% Cu, 4.4% Pb, 2.61% Zn and 29.39% Fe in tunnels, and 0.31 % Cu, 0.52% Pb, 6.29% Zn, 29.29% Fe, 0.03% Mo and 0.12% $WO_3$ in drill cores. Fluid inclusion data shows that Type I (liquid-rich), Type II (vapor-rich) and Type III (halite-bearing) inclusions are coexisted and their homogenization temperatures are quite similar. This indicates that boiling conditions have been reached during the mineralization. It is also likely that the ore solutions were evolved through the mixing between magmatic and meteoric waters. Rhyolite and quartz porphyry far the mineralization probably are not responsible of the Wondong polymetallic mineral deposits.

• Journal of the Mineralogical Society of Korea
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• v.13 no.4
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• pp.196-204
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• 2000

We present characteristics of hydrothermal chlorite and its interstratification with 7-$\AA$ mineral phase that occur in the propylitic alteration zone of the Bobae sericite deposit formed in rhyodacitic tuff. Chlorite is found as disseminated fine-grained aggregate or replacement materials of precursor minerals such as Fe-oxides and amphibole. Based on X-ray diffraction(XRD), all chlorites belong to IIb polytype and the (060) reflections averaging $1.53~1.54\AA$ indicate a trioctahedral structure. Chemical compositions of chlorite show that the Fe/(Fe+Mg) values are mostly in the range of 0.44~0.53, and cation deficiencies in octahedral sites range from 0.06 to 0.37. Under scanning electron microscope(SEM) chlorite occurs as well-crystallized aggregates and is subparallely stacked in interstices or between grain boundaries of associated minerals. transmission electron microscopic(TEM) images reveal that chlorite shows regular layers with $14-\AA$ spacings, locally interstratified with $7-\AA$ or $21-\AA$ periodicities. The $21- \AA$ periodicity corresponds to the sum of the $d_{001}$ values of chlorite and $7-\AA$ phase. The chlorite packet coexisting with 7-$\AA$ layers displays abundant defects such as edge dislocations and layer terminations. Selected-area electron diffraction(SAED) indicates that chlorite and $7-\AA$ phase are randomly interstratified in the mixed-layer areas. We propose a lateral change of layers for the polymorphic transition of $7-\AA$ phase to chlorite.e.

• Economic and Environmental Geology
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• v.25 no.2
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• pp.101-114
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• 1992

Occurrences of many kaolin-pyrophyllite deposits in the Youngnam area is related to the Late Cretaceous volcanic rocks, which are widely distributed through southern part from Tongnae-Yangsan to Miryang-Wolsung. The mode of occurrence and genesis of the kaolin-pyrophyllite deposits related to the volcanism was studied. This area is covered by andesitic rocks, rhyolite and rhyolitic welded tuff in ascending order. Lower most andesitic part is almost fresh. The altered rocks in the rhyolitic welded tuff can be classified into the following zones: silicified, pyrophyllite-kaolin, and argillic zone from the center part of ore deposit. The clay deposits occur as irregular massive, layer and funnel type about 5~20 m in width and is accompanied by thin diaspore bed outside of ore shoot. The clays chiefly consist of kaolinite, sericite, pyrophyllite, a little amount of diaspore, alunite, dumortierite, corundum and pyrite. The process of kaolinization-pyrophyllitization has a close relation to a local acidic hydrothermal solution originated from granitic rocks. Acidic hydothermal alteration occurrs mainly in the rhyolitic welded tuff. Initial solution containing $H_2S$ and others was oxidized near the surface and formed hydrothermal sulfuric acid solution.

• Economic and Environmental Geology
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• v.29 no.4
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• pp.411-419
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• 1996

The Janggun magnetite deposits occur as the lens-shaped magnesian skarn, magnetite and base-metal sulfide orebodies developed in the Cambrian Janggun Limestone Formation. The K-Ar age of alteration sericite indicates that the mineralization took place during late Cretaceous age (107 to 70 Ma). The ore deposition is divided into two stages as a early skarn and late hydrothermal stage. Mineralogy of skara stage (107 Ma) consists of iron oxide, base-metal sulfides, Mg-Fe carbonates and some Mg- and Ca-skarn minerals, and those of the hydrothermal stage (70 Ma) is deposited base-metal sulfides, some Sb- and Sn-sulfosalts, and native bismuth. Based on mineral assemblages, chemical compositions and thermodynamic considerations, the formation temperature, $-logfs_2$, $-logfo_2$ and pH of ore fluids progressively decreased and/or increased with time from skarn stage (433 to $345^{\circ}C$, 8.8 to 9.9 atm, 29.4 to 31.6 atm, and 6.1 to 7.2) to hydrothermal stage (245 to $315^{\circ}C$, 11.2 to 12.3 atm, 33.6 to 35.4 atm, and 7.3 to 7.8). The ${\delta}^{34}S$ values of sulfides have a wide range between 3.2 to 11.6‰. The calculated ${\delta}^{34}S_{H_2S}$ values of ore fluids are relatively homo-geneous as 2.9 to 5.4‰ (skam stage) and 8.7 to 13.5‰ (hydrothermal stage), which are a deep-seated igneous source of sulfur indicates progressive increasing due to the mixing of oxidized sedimentary sulfur with increasing paragenetic time. The ${\delta}^{13}C$ values of carbonates in ores range from -4.6 to -2.5‰. Oxygen and hydrogen isotope data revealed that the ${\delta}^{38}O_{H_2O}$ and ${\delta}D$ values of ore fluids decreased gradually with time from 14.7 to 1.8‰ and -85 to -73‰ (skarn stage), and from 11.1 to -0.2‰ and -87 to -80‰ (hydrothermal stage), respectively. This indicates that magmatic water was dominant during the early skarn mineralization but was progressively replaced by meteoric water during the later hydrothermal replacement.

• Journal of the Korean earth science society
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• v.29 no.7
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• pp.640-644
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• 2008

A type and origin of Buyeo and Jecheon mine as the domestic leading feldspar mines are classified by using the petrological characteristics. Jecheon mine is a weathered residual mine formed by the weathering of K-feldspar megacryst bearing porphyritic granite of which forming P-T is 840-5 Kb with the igneous origin of megacryst. On the other hand, Buyeo mine is made by the metasomatic alteration of hydrothermal solution from the biotite granite intrusion. Pure albite as a main ore mineral and garnet and sericite as accessaries are observed in this mine. In addition, the mine is typically characterized by the well recrystallized mineral texture.

• Journal of the Mineralogical Society of Korea
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• v.17 no.4
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• pp.339-355
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• 2004

Locality of domestic high-Ca limestones can be divided into three districts, i.e., (1) the Jecheon-Danyang area, (2) the Samcheok-Taebaek-Jungsun area, and (3) the Uljin-Andong area, in accordance with their geologic background and type of the deposits. Except for some crystalline limestones from the Jecheon-Danyang area, domestic high-Ca limestones were mostly recrystallized and Ca-enriched by the effects of hydrothermal alteration and/or thermal metamorphism. The lime-stones can be also divided into crystalline limestone type, marble type, micro- and mega-crystalline calcite types on the basis of their composition, crystallinity, and mineral facies. An applied-mineralogical characterization of the high-Ca limestones was done through the systematic analyses and tests for the limestones. The high-Ca limestones from the area (1), which are megascopic ally close to the original limestone in lithology, display lower whiteness, higher contents of CaO (51 ～ 54 wt.%), low crystallinity, and fine-grained texture. Two typical hydrothermal types of the high-Ca limestones from the area (2), i.e., micro- (mostly 0.2～0.3 mm) and mega-crystalline (2～15 em) calcite types, have comparatively higher whiteness and rather variable CaO contents (50～55 wt.%) with exhibiting quite different crystallinity each other. The micro-crystalline calcite type is especially dominant in this area, and has comparatively uniform crystallinity and homogeneous composition. Compared to these limestones, the high-Ca limestones from the area (3) show remarkable differences in grade and quality according to their types of deposit and occurrence. Based on these mineral characters and chemical composition, a possible scheme for industrial uses of the domestic high-Ca limestones was suggested.