• Economic and Environmental Geology
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• v.28 no.3
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• pp.185-197
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• 1995

Tungsten skarns in the Chungju mine which consists mainly of strata-bound type iron ore deposits are found in the vicinity of the contact between the age-unknown Kyemeongsan Formation and granitic rock intrusions of Mesozoic age($134{\pm}2Ma$). Tungsten skarns were formed extensively from alumina and silica-rich schistose rocks by the introduction of calcium and iron from hydrothermal solution. The skarns comprise a metasomatic column and are subdivided into four facies; garnet facies, wollastonite facies, epidote facies and chlorite facies. The skarn process in time-evolutional trend can be divided broadly into the four facies in terms of the paragenetic sequence of calc-silicates and their chemical composition. Skarn and ore minerals were formed in the following sequence; (1) garnet facies, adjacent to biotite granite, containing mainly garnet(>Ad96) and magnetite, (2) wollastonite facies containing mainly wollastonite and garnet(Ad95~60), (3) epidote facies, containing mainly epidote(Ps35~31), quartz, andradite-grossular(Ad63~50), and scheelite, (4) chlorite facies, adjacent to and replacing schist, containing mainly chrolite, muscovite, quartz, calcite, epidote(Ps31~25), hematite and sulfides. The mineral assemblage and mineral compositions. suggest that the chemical potentials of Ca and Fe increased toward the granitic rock, and the component Al, Mg, K, and Si decreased from the host rock to granitic rock. The homogenization temperature and salinity of fluid inclusion in scheelite, quartz and epidote of epidote facies skarn is $300-400^{\circ}C$ and 3-8wt.% eqiv. NaCl, respectively. ${\delta}^{34}S$ values of pyrite and galena associated with chlorite facies skarn is $9.13{\sim}9.51%_{\circ}$ and $5.85{\sim}5.96%_{\circ}$, respectively. The temperature obtained from isotopic com· position of coexisting pyrite-galena is $283{\pm}20^{\circ}C$. Mineral assemblages and fluid inclusion data indicate that skarn formed at low $X_{CO_2}$, approximately 0.01. Temperature of the skarn mineralization are estimated to be in the range of $400^{\circ}C$ to $260^{\circ}C$ and pressure to be 0.5 kbar. The oxygen fugacity($fo_2$) of the skarn mineralization decreased with time. The early skarn facies would have formed at log $fo_2$ values of about -25 to -27, and late skarn facies would have formed at log $fo_2$ values of -28 to -30. The estimated physicochemical condition during skarn formation suggests that the principal causes of scheelite mineralization are reduction of the ore·forming fluid and a decrease in temperature.

• Economic and Environmental Geology
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• v.55 no.2
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• pp.171-181
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• 2022

The Geochang Au-Ag deposit is located within the Yeongnam Massif. Within the area a number of hydrothermal quartz and calcite veins were formed by narrow open-space filling of parallel and subparallel fractures in the granitic gneiss and/or gneissic granite. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz vein; stage II, barren calcite vein) by major tectonic fracturing. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages (early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early, marked by deposition of pyrite with minor pyrrhotite and arsenopyrite; middle, characterized by introduction of electrum and base-metal sulfides with minor sulfosalts; late, marked by hematite with base-metal sulfides. Fluid inclusion data show that stage I ore mineralization was deposited between initial high temperatures (≥380℃ ) and later lower temperatures (≤210℃ ) from H₂O-CO₂-NaCl fluids with salinities between 7.0 to 0.7 equiv. wt. % NaCl of Geochang hydrothermal system. The relationship between salinity and homogenization temperature indicates a complex history of boiling, fluid unmixing (CO₂ effervescence), cooling and dilution via influx of cooler, more dilute meteoric waters over the temperature range ≥380℃ to ≤210℃. Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur by evolution of the Geochang hydrothermal system with increasing paragenetic time. The Geochang deposit may represents a mesothermal gold-silver deposit.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.753-765
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• 2021

The Dongwon Au-Ag deposit is located within the Paleozoic Taebaeksan province, Okcheon belt. Mineral paragenesis can be divided into two stages (stage I, ore-bearing quartz veins; stage II, barren carbonate veins) by major tectonic fracturing. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages(early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early, marked by deposition of pyrite with minor magnetite, pyrrhotite and arsenopyrite; middle, characterized by introduction of electrum and base-metal sulfides with minor sulfosalts; late, marked by argentite, Cu-As (and/or Sb) and Ag-Sb sulfosalts with base-metal sulfides. Fluid inclusion data show that stage I ore mineralization was deposited between initial high temperatures (≥430℃) and later lower temperatures (≤230℃) from fluids with salinities between 6.0 to 0.4 wt. percent equiv. NaCl. The relationship of salinity and homogenization temperature suggest that ore mineralization at Dongwon was deposited mainly due to fluid boiling, cooling and dilution via influx of cooler, more dilute meteoric waters. Changes in stage I vein mineralogy reflect decreasing temperature and fugacity of sulfur by evolution of the Dongwon hydrothermal system with increasing paragenetic time. The Dongwon deposit may represents a Korean-type and/or Au-Ag type mesothermal/epithermal gold-silver deposit.

• Economic and Environmental Geology
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• v.22 no.3
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• pp.253-266
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• 1989

The Cu-Pb-Zn-Ag hydrothermal vein type deposits which comprise the Dongil and Dong-cheogogsan mines occur within the Cretaceous sedimentary rocks in the Euiseong Basin of the southern Korean peninsula. The ore mineralization is contained within three stage(I,II and III) quartz and calcite veins. Ore minerals occur as dominant chalcopyrite, galena, sphalerite, tetrahedrite and Pb, Ag, Sb and Bi-bearing sulfosalts. Stage I ore minerals were deposited between $400^{\circ}C$ and $200^{\circ}C$ from the fluid with moderate salinities(7.0 to 4.5 eq. wt. % NaCl). Evidence of boiling suggests pressure of less than 150 bars during stage I mineralization. This pressure corresponds to maximum depths of 650 m and 1700 m, respectively, assuming lithostatic and hydrostatic loads. The data on mineralogy, temperature and salinity, together with information on the solubility of Cu complex, suggest that Cu deposition is a result of boiling coupled with declining temperature from $350^{\circ}$ to $250^{\circ}C$ or declining log $a_{o_2}$(from -29.8 to -35.9 atm.)and increasing in pH. Pb, Ag, Sb and Bi-bearing sulfosalts were deposited by cooling and dilution at temperature of less than $250^{\circ}C$ from the ore fluid with less than -35.9 atm. of log $a_{o_2}$.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.389-398
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• 1998

The Au-Ag deposit of the Oknam mine occurs as gold-silver-bearing rhodochrosite veins in biotite schist and phyllite of the Precambriam Yulri Group. Five stages of ore deposition are recognized, each showing a definite mineral assemblage. General mineral parageneses in veins (stage III) associated with gold and silver vary inwardly from the vein margin: arsenopyrite + pyrite $\Rightarrow$ sphalerite+chalcopyrite+galena+gold $\Rightarrow$ ga1ena+Ag-bearing minerals. Fluid inclusion data indicate that temperature and salinity of ore fluids overally decreased with time: $345^{\circ}{\sim}240^{\circ}C$ and 3.4~7.8 wt. % NaCl equiv during stage I (quartz vein mineralization), $313^{\circ}{\sim}207^{\circ}C$ and 2.3~8.7 wt.% NaCl equiv during manganese-bearing carbonate stages (II and III), and $328^{\circ}{\sim}213^{\circ}C$ and 3.6-5.4 wt.% NaCl equiv during stage IV (quartz vein mineralization). The ore fluids probably evolved through repeated pulses of boiling and later mixing with cooler and more dilute meteoric waters. Fluid inclusion data and geologic arguments indicate that pressures during the mineralization were in the range of 90 to 340 bars. Gold occurs as silver-rich electrums (21 to 29 atom. % Au) and was deposited at temperatures between $300^{\circ}$ and $240^{\circ}C$. Thermochemical calculations suggest that gold was deposited as a combined result of increase in pH and decreases in temperature, $fs_2$ and $fo_2$.

• Economic and Environmental Geology
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• v.29 no.6
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• pp.677-687
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• 1996

The Buckchang deposits which is located in the Ockcheon metamorphic zone, are emplaced along $N20-30^{\circ}E$ trending fissure sets. So it is a sort of fissure-filling ore deposits. The results of mineral paragenetic studies suggest two stages of hydrothermal mineralization; stage I: base-metal sulfides stage, stage II: late base-metal sulfides, electrum and silver-bearing sulfosalts stage. The silver-bearing sulfosalts occured as the Buckchang mine are mainly argentite and, minor of canfieldite, tetrahedrite, etc. Au:Ag ratios of the electrums show a highly limited range of nearly 1:1 in atomic %. The temperature, salinity and pressure of the Buckchang deposits estimated from fluid inclusion and sulfur isotope studies are as follows; stage I: $174{\sim}250^{\circ}C$, 0.35~4.01 NaCl eq. wt.%, 0.40~1.00 Kbar, stage II: $138{\sim}222^{\circ}C$, 1.9~8.4 NaCl eq. wt.%, 0.22~0.53 Kbar. The estimated oxygen and sulfur fugacity during stage I mineralization, based on phase relation of associated minerals, range from $10^{-39.7}{\sim}10^{-44.7}$ atm. and $10^{-13.4}{\sim}10^{-18.1}$ atm., respectively. All these evidences suggest that the Buckchang deposits are polymetallic epithermal ore deposits.

• Economic and Environmental Geology
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• v.49 no.6
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• pp.491-504
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• 2016

Jinwon Au-Ag deposit is located in the Uijin gun which is southeast 300 km from Seoul. The deposit area consists of mainly Precambrian Hongjesa granite, which occurs as porphyroblastic texture, medium grain and composed of quartz, feldspar and mica. This deposit consists of four parallel hydrothermal quartz veins that fill NE oriented fractures in Precambrian Hongjesa granite. The grade of quartz veins contain from 3.0 to 21.4 g/t (average 6.4 g/t) gold and from 5.0 to 252.0 g/t (average 117.9 g/t) silver, respectively. They vary from 0.2 m to 0.6 m (average 0.3 m) in thickness and extend to about 200 m in strike length. Quartz veins occur as massive, network, cavity, breccia, crustiform, comb and zonal textures. Wallrock alteration has silicification, sericitization, pyritization and argillitization. The mineralogy of the quartz veins consists of quartz, arsenopyrite, cassiterite, pyrite, sphalerite, chalcopyrite, galena, electrum, tetrahedrite, canfieldite, argentite, Ag-Sb-S mineral, Mn-Fe-O mineral, Pb-O mineral and Pb-P-Cl-O mineral(chloro-pyromorphite). Chemical compositions of minerals from this deposit are as followed; Fe/Fe+Mg of sericite is from 0.32 to 0.71, As content of arsenopyrite ranges from 27.91 to 30.33 atomic %, FeS content of sphalerite range from 9.77 to 16.76 mole %, Ag content of electrum is from 29.42 to 37.41 atomic % and Ag content of tetrahedrite range from 32.17 to 36.53 wt.%, respectively. Baased on mineralogy and chemical compositions of minerals from Jinwon Au-Ag deposit, deposition of minerals was caused by a change in temperature, oxygen fugacity($fO_2$) and sulfur fugacity($fS_2$) from the near neutral hydrothermal fluid evolved by reaction with wallrock.

• Economic and Environmental Geology
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• v.35 no.1
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• pp.1-12
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• 2002

Manus Basin, located in the equatorial western Pacific, is a back arc basin formed by collision between the IndoAustralian and the Pacific Plates. The basin is host to numerous hydrothermal vent fields and ore deposits. The basement rocks of the Manus Basin consist primarily of dacite and basaltic andesite. Some of the minerals that form the hydrothermal chimneys that were dredged on the Manus basin include pyrite, chalcopyrite, marcasite, sphalerite and galena. The chimneys can be classified into chalcopyrite dominant Cu-rich type and sphalerite dominant Zn-rich type. The concentration of Zn shows good positive correlation with that of Sb, Cd and Ag. The content of Cu, on the other hand, positively correlates with that of Mo, Mn and Co. For samples that were taken from Zn-rich chimney, a strong positive correlation is found between Au and Zn contents. The chimney also shows enrichments of Cd, Mn and Sb. On the other hand, the samples from Cu-rich chimney exhibit strong correlation among Au, Zn and Pb, and are enriched in Mo and Co concentration. Average contents of Au in Cu-rich and Znrich chimneys were 15.9 ppm and 29.0 ppm, respectively. Because of high concentration of Au with Ag and Cu, the ore deposit have high economic potential. Homogenization temperatures and salinities of fluid inclusions in anhydrite and amorphous silica from Zn-rich chimney are estimated to be l74-220$^{\circ}$C and 2.7-3.6 equiv. wt. % NaCI, respectively. These value suggest that ore forming processes were occurred at around 200$^{\circ}$C and that the oxygen fugacity changed from 2: 10$^{-39.5}$bar to -s: 10$^{-40.8}$bar and the sulfur fugacity from -s: 10$^{-14.7}$bar to 10$^{-13.4}$bar during the process. It appears that the temperature at which the ores formed on Cu-rich chimney was higher than that on Zn-rich chimney.

• Journal of the Mineralogical Society of Korea
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• v.23 no.1
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• pp.1-13
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• 2010

The Yugeum deposit in Youngduk in Gyungsangbuk-do is emplaced in the Cretaceous granitoids located in the Northeastem Gyeongsang Basin. Gold-bearing quartz veins filling the fracture with a direction of $N19^{\circ}{\sim}38^{\circ}W$ are most abundantly distributed within the Younghae granodiorite body. The formation of quartz veins can be classified into three main stages: barren quartz stage, auriferous quartz vein stage, and finally the extensive sulfide mineralization stage. Various sulfide minerals such as pyrite, chalcopyrite, galena, sphalerite, and arsenopyrite were precipitated during the hydrothermal gold mineralization process. Gold commonly occurs as fine-grained electrum in sulfides with high Au concentration (up to 93 wt%) compared to Ag. During the early gold mineralization stage, the temperature and pressure of the fluids are in the range of $220{\sim}250^{\circ}C$ and 730~1800 bar, and the oxygen fugacity is between $10^{-27}$ and $10^{-31.7}$ atm. On the other hand, the fluids of the late stage mineralization are characterized by temperature of $290{\sim}350^{\circ}C$ and pressure of 206~472 bar, and the oxygen fugacity is in the range of $10^{-26.3}{\sim}10^{-28.6}$ atm. The sulfur isotope compositions of sulfide minerals are in the range of $0.2{\sim}4.2^{\circ}/_{\circ\circ}$, while the ${\delta}^{34}SH_2S$ values range from 1.0 to $3.7^{\circ}/_{\circ\circ}$. The Ag/Au atomic ratios of electrum ranges from 0.15 to 1.10, and Au content is higher than Ag in most electrum. During the main gold mineralization stage at the relatively high temperature condition and with pH from 4.5 to 5.5, the stability of ${AuCl_2}^-$ increased while the stability of ${Au(HS)_2}^-$ decreased. Considering the pressure estimated in this deposit, the temperature of the ore fluid reached higher than $350^{\circ}C$ and ${AuCl_2}^-$ became an important species for the gold transportation. As mineralization proceeded with decreasing temperature and increasing pH and $f_{o2}$, the precipitation of sulfide minerals and accompanying electrum occurred.

• Economic and Environmental Geology
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• v.54 no.1
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• pp.49-60
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• 2021

The Geumhwa Au-Ag deposit is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into two stages (stage I and II) by major tectonic fracturing. Stage II is economically barren. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages(early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early substage, marked by deposition of pyrite with minor wolframite; middle substage, characterized by introduction of electrum and base-metal sulfides with Cu-As and/or Cu-Sb sulfosalts; late substage, marked by hematite and Bi-sulfosalts with secondary minerals. Changes in vein mineralogy reflect decreases in temperature and sulfur fugacity with a concomitant increase in oxygen fugacity. Fluid inclusion data indicate progressive decreases in temperature and salinity within each substage with increasing paragenetic time. During the early portion of stage I, high-temperature (≥410℃), high-salinity fluids (up to ≈44 equiv. wt. % NaCl) formed by condensation during decompression of a magmatic vapor phase. During waning of early substage, high-temperature, high-salinity fluids gave way to progressively cooler, more dilute fluids associated with main Au-Ag mineralization (middle) and finally to ≈180℃ and ≥0.7 equiv. wt. % NaCl fluids associated with hematite and sulfosalts (± secondary) mineralization (late substage). These trends are interpreted to indicate progressive mixing of high- and medium to low-salinity hydrothermal fluids with cooler, more dilute, oxidizing meteoric waters. The Geumhwa Au-Ag deposit may represent a vein-type system transitional between porphyry-type and epithermal-type.