• 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.

• Economic and Environmental Geology
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• v.9 no.1
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• pp.27-43
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• 1976

The flourite in Hwacheon, Hwanggangri and Keumsan district are major fluorite producing areas in Korea. The fluorite deposits of Hwacheon district are wholly fissure filling hydrothermal veins embedded in Precambrian gneiss and schists and Jurassic granites. Also some fluorite deposits are emplaced in felsite whose age is unknown. Emplacement of most fluorite veins of the district are controlled by EW fracture system. Fluorites are generally accompanied to chalcedonic quartz and also kaolinite, montmorillonite, dickite and calcite in parts. Vertical and lateral mineral zonings are not distinct. The fluorite deposits in the Hwanggangri district are wholly embedded in limestone and other calcareous sediments of Paleozoic Yeongweol Group. Most of the fluorite deposits belong to one of two categories which are steeply. dipping veins and gently dipping replacement deposits adjacent to Late Cretaceous(83-90mys) granite bodies. The strikes of fluorite veins of Hwanggangri district mostly occupy the fractures of $N30^{\circ}-40^{\circ}E$ and $N30^{\circ}-40^{\circ}W$ system. Fluorites are accompanied to calcite, milky quartz, chalcedonic quartz, and also montmorillonite, kaolinite in parts. But in some deposits, scheelite, various sulfide minerals and barite are accompanied. Emplacement of fluorite deposits are largely controlled by lithology and structures of this district. In some deposits fluorite veins gradate to scheelite veins and also telescoping of the mineral zones are found in this district. In the Keumsan district, fissure-filled fluorite veins and replacement deposits are mostly emplaced in limestone of Paleozoic Yeongweol Group, late Cretaceous quartz-porphyry, granite and sandstone. Some deposits are emplaced in Precambrian metasediments. Mineralogy and other characteristics of the deposits in this district is similar to those of Hwanggangri district. Fluid inclusion studies reveal the difference of salinities, $CO_2$ contents of ore fluid and temperatures during fluorite mineral deposition in the these districts. In Hwacheon district, ore-fluids were comparatively dilute brine and low $CO_2$ content. Filling temperatures ranges $104^{\circ}C$ to $170^{\circ}C$. In the Chuncheonshinpo mine, most deeply exploited one in this district, salinitles range 0.5-2. 2wt. % NaCl and filling temperatures range from $116^{\circ}C$ to $143^{\circ}C$. In the Hwanggangri district, ore fluids were complex and filling temperature ranges very widly. In the contact metasomatic fluorite deposits, ore fluid were NaCl rich brines with moderate $CO_2$ content and filling temperatures range from $285^{\circ}C$ to above $360^{\circ}C$. Fluids inclusions in tungsten and sulfide minerals bearing fluorite veins show high $CO_2$ content up to 31wt. %. Filling temperature ranges from $101^{\circ}C$ to $310^{\circ}C$. Fluids inclusions In mainly fluorite bearing veins were more dilute brine and low $CO_2$ contents. Filling temperatures range from $95^{\circ}C$ to $312^{\circ}C$. Filling temperature of fluid inclusions of Keumsan district are between $95^{\circ}C$ and $237^{\circ}C$. Data gathered from geologic, mineralogic and fluid inclusion studies reveal that fluorite mineralization in H wacheon district proceeded at low temperature with dilute brine and low $CO_2$ content. In Hwangganri district, fluorite mineralization proceeded by several pulse of chemically distinct ore fluids and formed the mineralogically different type of deposits around cooling granite pluton which emplaced comparatively shallow depth.

• Economic and Environmental Geology
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• v.21 no.1
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• pp.45-56
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• 1988

Many hydrothermal skarn-type iron ore deposits inchiding Mulgeum, Yangseong, Maeri and Kimhae mines are distributed in the south-eastern Gyeongnam Province, Korea. The deposits are magnetite veins which occurred in propylitized andesitic rock near the contact with late Cretaceous Masanite. Symmetrical zoned skarns are commonly developed around the magnetite veins. The order of the skarn zones from the vein is garnet-quartz skarn, epidote skarn, and epidote-orthoclase skarn. The garnets include isotropic or anisotropic andradite($Ad_{100{\sim}70}$), and the epidotes are composed of pistacite($Ps_{21-31}$). Fe contents of the epidotes generally increase toward the magnetite veins. Epidotes and garnets often show compositional variations from grain to grain, that is, their Fe and Al contents vary inversely. This suggests that the variations depend mainly upon $fo_2$ during the skarnization. Oxygen and carbon isotope analyses of minerals from andesitic rock, micrographic granite, major skarn zones and post-mineralization zones were conducted to provide the information on the formation temperature, the origin and the evolution of the hydrothermal solution forming the iron ore deposits. Becoming more distant from the ore vein, temperatures of skarn zones represent the decreasing tendency, but most ${\delta}O^{18}$ and ${\delta}O^{18}_{H_2O}$ values of skarn minerals represent no variation trend, and also the values are relatively low. Judging from all the isotopic data from the ore deposits, the major source of hydrothemal solution altering the skarn zones and precipitating the ore bodies was magmatic water derived from the more deeply seated micrographic granite. This high temperature hydrothermal solution rising through the fissures of propylitized andesitic rock was mixed with some meteoric water, and the extensive isotopic exchange occurred with the propylitized andesitic rock. During this process, the temperature and ${\delta}O^{18}_{H_2O}$ value of hydrothermal solution were lowered gradually. At the stage of iron ore precipitation, because after all the alteration was already finished, the oxygen isotopic exchange with the wall rock was nearly not taken. The relatively high ${\delta}O^{18}$ and ${\delta}O^{18}_{H_2O}$, and relatively low ${\delta}C^{13}$ values of calcites of post mineralization stage, are the results of leaching of the high ${\delta}O^{18}$ chert xenolith in the andesitic rock and low ${\delta}C^{13}$ andesitic rock.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.205-214
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• 2005

Some Quaternary faults developed in the eastern block of the Ulsan fault are Gaegok 1, Gaegok 2, Singye, Madong, Wonwonsa and Jinhyeon faults, which are characterized by thin gouge and narrow cataclasitic tones. This study was performed to emphasize the role of mineral alteration and microtexture in response to hydrothermal alteration of fault gouges during fault activity, using XRD, EPMA, BSE (backscattered electron image), and K-Ar age dating methods. Alteration minerals in fault gouges were formed in the age range of $44.3\~28.9Ma$ by hydrothermal alteration attributed to fault activity. XRD results show that fault gouges consist predominantly of clay minerals, quartz and feldspars. Clay minerals formed in the gouge zones are mainly composed of smectite with trace chlorite, illite and kaolinite. The evidence to support the hydrothermal alteration of preexisting minerals due to fault activity are easily recognized at the host rocks in contact with gouges zones. Injected gouge and calcite veins indicate that they were originated from multiple deformation by repeated fault activity. Gouge with green or greenish grey color, for example Jinhyeon fault, contains higher $Al_2O_3$ and lower MgO and CaO compared to those with reddish color. Various colors of fault gouge are intimately related to the chemical compositions of main constituent mineral as well as mineral assemblage.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.2
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• pp.125-134
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• 2023

The Naedeokri and Nonggeori granites are early Proterozoic granites of the Taebaek-Sangdong area in the northeastern part of the Yeongnam Massif. In this paper, rare earth elements (REEs) concentrations of the minerals in Naedeokri and Nonggeori granites and Rb-Sr mineral isochron age are reported. Except zircon, the constituent minerals such as mica, feldspar, quartz, and tourmaline show LREE-enriched and HREE-depleted REE patterns with relatively large Eu negative anomaly. However, zircon has geochemical characteristic of LREE- and HREE-enriched REE pattern with large Eu positive anomaly. This pattern suggests that zircon should be hydrothermal zircon due to deuteric hydrothermal alteration. In addition, the Rb-Sr mineral age of Naedeokri granite indicates an age value of 1.814±142(2σ) Ma. The Rb-Sr whole rock age including pervious data of Naedeokri and Nogggeori granite indicates an age value of 1,707±74(2σ) Ma. This value is younger than the Sm-Nd isochron of 1.87 Ga, indicating that the Rb-Sr isotope system may be re-homogenized by hydrothermal alteration during the transition from a magmatic to a hydrothermal system.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.2
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• pp.115-127
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• 2020

The Unsang gold deposit has been one of the three largest deposits (Daeyudong and Kwangyang) in Korea. The deposit consists of Au-bearing quartz veins filling fractures along fault zones in Precambrian metasedimentary rock and Jurassic Porphyritic granite, which suggests that it might be an orogenic-type. Based on its mineral assemblages and quartz textures, quartz veins are classified into 1)galena-quartz, 2)pyrrhotite-quartz, 3)pyrite-quartz, 4)pegmatic quartz, 5)muscovite-quartz, and 6)simple quartz vein types. The pyrite-quartz vein type we studied shows the following alteration features: sericitization, chloritization, and silicification. The quartz vein contains minerals including white quartz, white mica, chlorite, pyrite, rutile, calcite, monazite, zircon, and apatite. Rutile with euhedral or medium aggregate occur at mafic part from laminated quartz vein. Two types of rutile are distinguishable in BSE image, light rutile is texturally later than dark rutile. Chemical composition of rutile has 89.69~98.71 wt.% (TiO₂), 0.25~7.04 wt.% (WO₃), 0.30~2.56 wt.% (FeO), 0.00~1.71 wt.% (Nb₂O₅), 0.17~0.35 wt.% (HfO₂), 0.00~0.30 wt.% (V₂O₃), 0.00~0.35 wt.% (Cr₂O₃) and 0.04~0.25 wt.% (Al₂O₃), and light rutile are higher WO₃, Nb₂O₅ and FeO compared to the dark rutile. It indicates that dark rutile and light rutile were formed at different stage. The substitution mechanisms of dark rutile and light rutile are suggested as followed : dark rutile [(V³⁺, Cr³⁺) + (Nb⁵⁺, Sb⁵⁺) ↔ 2Ti⁴⁺, 4Cr³⁺ (or 2W⁶⁺) ↔ 3Ti⁴⁺ (W⁶⁺ ↔ 2Cr³⁺), V⁴⁺ ↔ Ti⁴⁺], light rutile [2Fe³⁺ + W⁶⁺ ↔ 3Ti⁴⁺, 3Fe²⁺ + W⁶⁺ ↔ Ti⁴⁺ + (V³⁺, Al³⁺, Cr³⁺) +Nb⁵⁺], respectively. While the dark rutile was formed by cations including V³⁺, V⁴⁺, Cr³⁺, Nb⁵⁺, Sb⁵⁺ and W⁶⁺ by regional metamorphism of hostrock, the postdating light rutile was formed by redistribution of cations from predating dark rutile and addition of Fe²⁺ and W⁶⁺ from Au-bearing hydrothermal fluid during ductile shear.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.505-517
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• 1997

Lead and zinc mineralization of the Kwangsin mine was formed in quartz and carbonate veins that filled fault-related fractures in the limestone-rich Samtaesan Formation of the Chosun Supergroup and the phyllite-rich Suchangni Formation of unknown age. A K-Ar date of alteration sericite indicates that the Pb-Zn mineralization took place during Late Cretaceous (83.5 Ma), genetically in relation to the cooling of the nearby Muamsa Granite (83~87 Ma). Mineral paragenesis can be divided into three stages (I, II, III): (I) the deposition of barren massive white quartz, (II) the main Pb-Zn mineralization with deposition of white crystalline quartz and/or carbonates (rhodochrosite and dolomite), and (III) the deposition of post-ore barren calcite. Mineralogic and fluid inclusion data indicate that lead-zinc minerals in middle stage II (IIb) were deposited at temperatures between $182^{\circ}$ and $276^{\circ}C$ from fluids with salinities of 2.7 to 5.4 wt. % equiv. NaCl and with log $fs_2$ values of -15.5 to -11.8 atm. The relationship between homogenization temperature and salinity data indicates that lead-zinc deposition was a result of fluid boiling and later meteoric water mixing. Ore mineralization occurred at depths of about 600 to 700 m. Sulfur isotope compositions of sulfide minerals (${\delta}^{34}S_{CDT}=9.0{\sim}14.5$ ‰) indicate a relatively high ${\delta}^{34}S_{{\Sigma}S}$ value of ore fluids (up to 14 ‰), likely indicating an igneous source of sulfur largely mixed with an isotopically heavier sulfur source (possibly sulfates in surrounding sedimentary rocks). There is a remarkable decrease of calculated ${\delta}^{18}O$ value of water in hydrothermal fluids with increasing paragenetic time: stage I, 14.6~10.1 ‰; stage IIa, 5.8~2.2 ‰; stage IIb, 0.8~2.0 ‰; stage IIc, -6.1~-6.8 ‰, This indicates a progressive increase of meteoric water influx in the hydrothermal system at Kwangsin. Measured and calculated hydrogen and oxygen isotope values indicate that the Kwangsin hydrothermal fluids was formed from a circulating (due to intrusion of the Muamsa Granite) meteoric waters which evolved through interaction mainly with the Samtaesan Formation (${\delta}^{18}O=20.1$ to 24.9 ‰) under low water/rock ratios.

• Economic and Environmental Geology
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• v.46 no.1
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• pp.11-19
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• 2013

The Daehwa Mo-W deposit is located within the Gyeonggi massif. Quartz and calcite vein mineralization occurred in the Precambrian gneiss and Jurassic granites. Three main types (Type I: liquid-rich $H_2O$ type, Type II: vapor-rich $H_2O$ type, Type III: $CO_2-H_2O$ type) of fluid inclusions were observed and are classified herein based on their phase relations at room temperature. Within ore shoots, type III fluid inclusions have been classified into four subtypes (type IIIa, IIIb, IIIc and IIId) based on their volume percent of aqueous and carbonaceous ($CO_2$) phase at room temperatures combined with their total homogenization behavior and homogenization behavior of $CO_2$ phase. Homogenization temperatures of primary type I fluid inclusions in the quartz range from $374^{\circ}C$ to $161^{\circ}C$ with salinities between 13.6 and 0.5 equiv. wt.% NaCl. Homogenization temperatures of primary type III fluid inclusions in quartz of main generation, are in the range of $303^{\circ}C$ to $251^{\circ}C$. Clathrate melting temperatures of the type III fluid inclusions were 7.3 to $9.5^{\circ}C$, corresponding to salinities of 5.2 to 1.0 equiv. wt. % NaCl. Melting and homogenization temperatures of $CO_2$ phase of type III fluid inclusions were -57.4 to $-56.6^{\circ}C$ and 29.0 to $30.8^{\circ}C$, respectively. Fluid inclusion data indicate a complex geochemical evolution of hydrothermal fluids. The Daehwa early hydrothermal system is characterized by $H_2O-CO_2$-NaCl fluid at about $400^{\circ}C$. The main mineralization occurred by $CO_2$ immiscibility at temperatures of about 300 to $250^{\circ}C$. At the late base-metal mineralization aqueous fluid formed by mixing with cooler and less saline meteoric groundwater.

• Economic and Environmental Geology
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• v.28 no.1
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• pp.25-31
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• 1995

In Dongnam area, Cretaceous igneous rocks, such as diorite, porphyritic granite, and quartz porphyry intruded Paleozoic sedimentary rocks, such as Myobong slate and Pungchon limestone. The Dongnam Fe-Mo skarn deposits were imposed on the diorite(endoskarn) and the Myobong slate(exoskarn). The ore deposits consist mainly of magnetite and molybdenite with small amounts of sulfides, such as galena, sphalerite, pyrite, chalcopyrite, and pyrrhotite. The igneous rocks show nearly constant $^{206}Pb/^{204}Pb(18.80{\sim}19.06)$ and $^{207}Pb/^{204}Pb(15.71{\sim}15.72)$ ratios. Their $^{207}Pb/^{204}Pb$ ratios higher than the typical ratios of orogene suggest that the igeneous rocks were formed from lower crust(or mantle) - derived magma excessively contaminated by upper crustal materials such as high radiogenic Precambrian basement rocks. The lead isotopic compositions of the igneous rocks, the Pungchon limestone, and the ore minerals show a well defined linear in $^{206}Pb/^{204}Pb$ - $^{207}Pb/^{204}Pb$ plot. The lead isotopic compositions of the igneous rocks are similar to those of magnetite and galena, which were formed at early skarn stage and significantly lower than those of altered quartz porphyry, molybdenites, and pyrite, which were formed at late epithermal alteration stage. Considering the systematic variation of the lead isotopic compositions in the ore minerals according to hydrothermal stages, the variation may be due to a relative variation in surrounding rock(Pungchon limestone) involvement in hydrothermal ore solution leaching the surrounding rock. Therefore, the variation of the lead isotopic compositions in ore minerals can be modeled in terms of the mixing of the leads derived from the igneous rocks as low radiogenic source and the surrounding rock(Pungchon limestone) as high radiogenic source.

• Economic and Environmental Geology
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• v.26 no.3
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• pp.337-347
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• 1993

Mineralogical and geochemical studies on some pyrophyllite deposits in Milyang area, Kyeongnam Province (Milyang and Sungjin mine) were carried out in order to investigate dispersion patterns of chemical elements in altered volcanic wallrocks, and to interpret genetic environments of the pyrophyllite deposits. Cretaceous andesitic and tuffaceous rocks, and pyrophyllite ore specimens were collected from the dumps and drilling cores. Andesitic wallrocks were grouped as unaltered and altered rocks in the order of pyrophyllitization. Vertical dispersion patterns and relative mobilities of chemical elements in volcanic wallrocks were discussed. Geochemical environment in the Milyang area is characterized by the occurrence of boron minerals such as dumortierite coexisting with pyrophyllite ores, and tourmaline in granitic rocks. Unaltered andesitic rocks are mainly composed of plagioclase, pyroxene and hornblende, and were propylitized and saussuritized. Altered andesitic rocks are bleached and consist of quartz, sericite, pyrophyllite, kaolinite, chlorite and disseminated pyrite. Pyrophyllite ores are mainly composed of quartz, pyrophyllite, dumortierite, dissemianted pyrite and some diaspore. Enrichment of $SiO_2$, $Al_2O_3$, LOI (loss on ignition), As and Cr, and depletion of $K_2O$, $Na_2O$, CaO, MgO and total Fe are characteristic during alteration process. The REE patterns show that the pyrophyllite deposits could be originated from the continental margin volcanics. The $(La/Lu)_{cn}$ ratios of the pyrophyllite ores increase from 4.2~23.2 to 2.67~128.8 owing to strong acidic hydrothermal alteration. Vertical dispersion patterns of $Al_2O_3$, $K_2O$, $Na_2O$, CaO, MgO, $Fe_2O_3$ (total Fe), As, Au, Sb, Cr and Sr in the wallrocks show the location of orebodies. Particularly dispersion patterns of $Al_2O_3$ and Cr indicate the extension of orebodies. Anomalous distribution of Au, As and Sb in wallrocks shows potential for gold occurrence below the pyrophyllite deposits. Judging from the relative mobilities of elements in wallrocks, $Al_2O_3$ could be added from hydrothermal solution, and the silicified rone be formed from the excess of $SiO_2$.