• Economic and Environmental Geology
• /
• v.19 no.1
• /
• pp.1-18
• /
• 1986

A group of 16 $Zn+Pb{\pm}Ag$ deposits distributed in the Pyeongchang-Jucheon area, Kangwon-do, South Korea, were semi-regionally investigated. These deposits are contact metasomatic and/or hydrothermal replacement types hosted in the carbonate-dominated Cambrian Machari Formation and Ordovician Ibtanri Formation, and also in the carbonate interbeds of the Precambrian argillic metasediments. Comparing some key aspects of the individual deposits, it is found that the ore deposits hosted in the Machari and Ibtanri Formations are mostly of steeply-dipping chimneys with or without skarn minerals and are rich in Ag and Pb>Zn in metal grade whereas those occuring in the carbonate interbeds of the Precambrian argillic metasediments are gently-dipping conformable lenticular orebodies mostly with skarn minerals and are generally poor in Ag and Zn>Pb. The skarn mineralization in the area appears to have occurred during the lower Cretaceous (118.7Ma) to mid-Cretaceous (107.8Ma) time assumed from the K-Ar dates of the Dowon and Pyeongchang granites which are closely associated with the skarn ore deposits. The Rb/Ba/Sr ratios of these granites indicate that they are of strongly differentiated anomalous granites, and the Nb vs. Y and Rb vs. Y+Nb plots fall on the field of volcanic arc setting. The contact aureoles are zoned, giving the sequence in order of increasing distance from igneous contact: garnet-wollastonite, granet-wollastonite-clinopyroxene and garnet-clinopyroxene in such as the Pyeongchang and Yeonwol 114 areas. Electron microprobe analyses reveal that garnets and clinopyroxenes are generally low in Fe and Mn. Garnets are grossular to intermediate grandite except for those from the Ogryong exoskarn which are richer in andradite, pyrope and spessartine fractions. This indicates that the oxidation state of skarn-forming environment at Ogryong was higher than at the other deposits. Clinopyroxenes are mostly salitic except for those from the Ogryong exoskarn which involve considerable amounts of hedenbergite and johansenite fractions. The ${\delta}^{18}O$ value of Jurassic biotite granite at Ogryong is higher (+10.21‰) than that of Cretaceous one at Chodun (+8.41‰). The ${\delta}^{13}C$ values of carbonate rocks range from -0.89‰ to 0.68‰ and the ${\delta}^{18}O$ values range from +11.91‰ to + 19.34‰ indicating that these carbonate rocks are of marine origin. However, the ${\delta}^{13}C$ values of skarn calcite and vein calcite are -4.80‰ and -12.92‰, and the ${\delta}^{18}O$ values are +5.56‰ and +10.32‰, respectively, indicating that these calcites are of hydrothermal origin. The ${\delta}^{34}S$ values of sulfide minerals range from +4.4‰ to +8.7‰ suggesting that the sulfurs are of magmatic origin.

• Economic and Environmental Geology
• /
• v.26 no.1
• /
• pp.41-54
• /
• 1993

The Ulsan Fe-W deposit, which can be classified as a calcareous skarn deposit, is represented by ore pipe consisting principally of magnetite and lesser amounts of scheelite with minor sulphides, sulphosaits, arsenides, sulpharsenides, etc. At Ulsan mine, metasomatic processes of skarn growth may be divided broadly into two stages based on the paragenetic sequence of calc-silicate minerals and their chemical composition; early and late skarn stages. Early stage has started with the formation of highly calcic assemblages of wollastonite, diopsidic clinopyroxene and nearly pure grossular, which are followed by the formation of clinopyroxenes with salite to ferrosalite composition and grandite garnets with intermediate composition. Based on these calc-silicate assemblages, the temperatures of early skarn formations have been in the ranges of $550^{\circ}$ to $450^{\circ}$. The calc-silicate assemblages formed during the earlier half period of late skarn stage show the enrichment of notable iron and slight manganese, and the depletion of magnesium; clinopyroxenes are hedenbergitic, and grandite garnets are andraditic. The formation temperatures during this skarn stage are inferred to have been in the range of $430^{\circ}$ to $470^{\circ}C$ at low $X_{CO_2}$ by data from fluid inclusions of late andraditic garnets. The later half period of late skarn stage is characterized by the hydrous alteration of pre-existing minerals and the formation of hydrous silicates. The main iron-tungsten mineralization representing prominent deposition of magnetite immediately followed by minor scheelite impregnation has taken place at the middle of early skarn stage, while complex polymetallic mineralization has proceeded during and after the late skarn stage. Various metals and semimetals of Fe, Ni, Co, Cu, Zn, As, Mo, Ag, In, Sn, Sb, Te, Pb and Bi have been in various states such as native metal, sulphides, arsenides, sulphosaits, sulpharsenides and tellurides.

• Journal of the Mineralogical Society of Korea
• /
• v.23 no.4
• /
• pp.413-428
• /
• 2010

The Gukjeon Pb-Zn mine was recognized as skarn deposits which replaced the limestone layer of the Jeongkansan Formation by intrusion of biotite granite in late Cretaceous. The Jeongkansan Formation is mainly composed of tuffaceous shale, and interlayers of sandstone, andesitic tuff, limestone, and conglomerate. The limestone layer is located in the lower part of the Jeongkansan Formation with 6~8 m in thickness and about 500 m in length. The Gukjeon deposits are divided into the Jukgang ore bodies once mined underground and the eastern ore bodies. Main ores are sphalerite and galena, in association with small amounts of chalcopyrite, arsenopyrite, pyrite, and pyrrhotite, etc. Skarns mainly consist of clinopyroxenes and Ca-garnets, associated with actinolite, chlorite, axinite, and calcite, etc. The Jukgang ore bodies show symmetrical distribution of zoning outward, representing clinopyroxene (hedenbergite) zone, clinopyroxene-garnet (grossular) zone, garnet (andradite) zone, and alteration zone of hornfels. $Fe^{2+}$ contents in clinopyroxenes increase with decreasing sphalerite grade. Sphalerite ores are found in all zones and $Fe^{2+}$ contents in sphalerite increase in the same way as those in clinopyroxenes, implying that clinopyroxene and sphalerite are closely related each other. It is concluded that the Gukjeon ores occurred in the ore rich zone of high grade sphalerite with less pyrite in assoication with clinopyroxene.

• Economic and Environmental Geology
• /
• v.47 no.4
• /
• pp.335-349
• /
• 2014

The Pocheon skarn deposit, located at the northwestern part of the Precambrian Gyeonggi massif in South Korea, occurs at the contact between the Cretaceous Myeongseongsan granite and the Precambrian carbonate rocks, and is also controlled by N-S-trending shear zone. The skarn distribution and mineralogy reflects both structural and lithological controls. Three types of skarn formations based on mineral assemblages in the Pocheon skarn exist; a sodiccalcic skarn and a magnesian skarn mainly developed in the dolostone, and a calcic skarn developed in the limestone. Iron mineralization occurs in the sodic-calcic and magnesian skarn zone, locally superimposed by copper mineralization during retrograde skarn stage. The sodic-calcic skarn is composed of acmite, diopside, albite, garnet, magnetite, maghemite, anhydrite, apatite, and sphene. Retrograde alteration consists of tremolite, phlogopite, epidote, sericite, gypum, chlorite, quartz, calcite, and sulfides. Magnesian skarn mainly consists of diopside and forsterite. Pyroxene and olivine are mainly altered to tremolite, with minor phlogopite, talc, and serpentine. The calcic skarn during prograde stage mainly consists of garnet, pyroxene and wollastonite. Retrograde alteration consists of epidote, vesuvianite, amphibole, biotite, magnetite, chlorite, quartz, calcite, and sulfides. Microprobe analyses indicate that the majority of the Pocheon skarn minerals are enriched by Na-Mg composition and have high $Fe^{3+}/Fe^{2+}$, $Mg^{2+}/Fe^{2+}$, and $Al^{3+}/Fe^{2+}$ ratios. Clinopyroxene is acmitic and diopsidic composition, whereas garnet is relatively grossular-rich. Amphiboles are largely of tremolite, pargasite, and magnesian hastingsite composition. The prograde anhydrous skarn assemblages formed at about $400^{\circ}{\sim}500^{\circ}C$ in a highly oxidized environment ($fO_2=10^{-23}{\sim}10^{-26}$) under a condition of about 0.5 kbar pressure and $X(CO_2)=0.10$. With increasing fluid/rock interaction during retrograde skarn, epidote, amphibole, sulfides and calcite formed as temperature decreased to approximately $250^{\circ}{\sim}400^{\circ}C$ at $X(CO_2)=0.10$.

• Economic and Environmental Geology
• /
• v.47 no.4
• /
• pp.363-379
• /
• 2014

The Haenam Pb-Zn skarn deposit is located at the Hwawon peninsula in the southwestern part of the Ogcheon Metamorphic Belt. The deposit is developed along the contact between limestone of the Ogcheon group and Cretaceous quartz porphyry. Petrography of ore samples, chemical composition of skarn and ore minerals, and geochemistry of the related igneous rocks were investigated to understand the characteristics of the skarn mineralization. Skarn zonation consists of garnet${\pm}$pyroxene${\pm}$calcite${\pm}$quartz zone, pyroxene+garnet+quartz${\pm}$calcite zone, calcite+pyroxene${\pm}$garnet zone, quartz+calcite${\pm}$pyroxene zone, and calcite${\pm}$chlorite zone in succession toward carbonate rock. Garnet commonly shows zonal texture comprised of andradite and grossular. Pyroxene varies from Mn-hedenbergite to diopside as away from the intrusive rock. Chalcopyrite occurs as major ore mineral near the intrusive rock, and sphalerite and galena tend to increase as going away. Electron probe microanalyses revealed that FeS contents of sphalerite become decreased from 5.17 mole % for garnet${\pm}$pyroxene${\pm}$calcite${\pm}$quartz zone to 2.93 mole %, and to 0.40 mole % for calcite+pyroxene${\pm}$garnet zone, gradually. Ag and Bi contents also decreased from 0.72 wt.% and 1.62 wt.% to <0.01 wt.% and 0.11 wt.%, respectively. Thus, the Haenam deposit shows systematic variation of species and chemical compositions of ore minerals with skarn zoned texture. The related intrusive rock, quartz porphyry, expresses more differentiated characteristics than Zn-skarn deposit of Meinert(1995), and has relatively high$SiO_2$ concentration of 72.76~75.38 wt.% and shows geochemical features classified as calc-alkaline, peraluminous igneous rock and volcanic arc tectonic setting.

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

• The Journal of the Petrological Society of Korea
• /
• v.7 no.2
• /
• pp.111-131
• /
• 1998

The migmatitic gneiss in the Odesan Gneiss Complex has small amount of quartzite, amphibolite and marble and the Kuryong Group which contact with migmatitic gneiss unconformitly, also contains some amphibolite. Preview studies of this area had regarded that the amphibolites contact with marble had been produced by metasomatism from the pelitic and calcareous sediments mixtures, but the amphibolite is reinterpreted as igneous origin. $SiO_2$ content of the amphibolite is 45.9~52.7 wt%, which corresponds to basaltic composition. MgO content has narrow range (4.6~6.87 wt%) and major and trace element are plotted against MgO,$TiO_2, P_2O_5$, Hf, Zr are reduced and Cr and Ni are increased their content with increasing MgO. This phenomenon indicates that the basaltic magma as the protolith of the amphibolite had frationated with the crystallization of the pyroxene and/or olivine. REE pattern has smoothly decrease from LREE to HREE. Eu/Eu(0.83~1.19) show the flat Eu anomaly, which indicate small fractional crystallization of plagioclase. HREE is enriched in the garnet-bearing amphibolites. Several discrimination diagram for the basaltic magma show that the amphibolite of the study area is originated tholeiitic basaltic magma indicating continental rift environment. Due to determine the metamorphic condition garnet-hornblende geothermometry and hornblende-plagioclase geobarometry are used. Peak metamorphic temperature range of the amphibolite $788~870^{\circ}C$ and is deduced toward the northeastern part. The calculated temperature from the amphibolite has slightly higher than the temperature of the metapelites but the trend of metamorphic grade which decrease from western to eastern part progradly is similar to each other. The metamorphic pressure calculated by garnet- hornblede-plagioclase geobarometry is 4~5kb. But ilmenite-plagioclase pair enclosed in garnet show 8 kb at $700^{\circ}C$ by garnet-ilmenite-rutile-plagioclase geobarometery. The zonal profile of garnet in sample 84 shows the bell-shape profile, which grossular content decreases whereas pyrope content increases progressively. This means that the amphibolite has undergone the clockwise P-T-t path which is shown in the migmatitic gneiss of the Odesan Gneiss Complex.

• Economic and Environmental Geology
• /
• v.12 no.2
• /
• pp.51-73
• /
• 1979

The zinc-lead deposits at the Yeonhwa I mine were investigated in terms of ore-forming geologic setting, structural style of ore control, geometry of individual orebodies, zoning, paragenesis and chemical composition of skarn minerals, as well as metal grades and ratios of selected orebodies. The Yeonhwa I mine is characterized by a large swarm of chimney type massive orebodies with thin skarn envelopes, boldly developed through a thick sequence of Pungchon Limestone, the overlying Hwajeol Formation, and the underlying Myobong Slate of Cambrian age. Nearly 20 orebodies of similar shape, but of varying size are arranged in a V-shaped pattern with northwest and northeast trends, clearly indicating an outstanding ore control by a conjugate system of fractures with these trends. Important orebodies are the Wolam 1, 2, 3, and 5 orebodies in the west, and the Namsan 1, 2, 3. and 5 orebodies in the east, among others. The Wolam 1 orebody, which was observed from the -360 level through the -240, -120, and 0 levels to the surface outcrops (totaling a vertical height of about 500m), shows a vertical variation in skarn mineralogy, ranging from pyroxene-garnet zone on the lower levels. through pyroxene (without garnet) zone on the intermediate levels, and finally to rhodochrosite vein on the upper levels and surface. Microprobe analyses of pyroxene and garnet on a total of 14 mineral grains revealed that pyroxenes are manganoan salitic in most samples, with downward increase of Fe and Mn, whereas garnets are highly andraditic, containing fractions of subordinate grossular with downward decrease of Fe. This indicates a reverse relationship of Fe-contents between pyroxene and garnet with depth. Ore minerals are major sphalerite, subordinate galena, and minor chalcopyrite. Sulfide gangue minerals include major pyrrhotite, and minor pyrite and marcasite of later age. Two types of variational trends in metal grades and ratios with depth are present on the plots of assay data from the Wolam orebodies: one is a steady upward increase in Pb, Zn, and Pb:Zn ratios, with a terminal decline at the top of orebody: the other is an irregular or sinusoidal change. The former is characteristic of chimney-type orebodies, whereas the latter is of vein· shaped orebodies. The Pb grades show large variations among orebodies and from level to level, whereas the Zn grades are relatively constand or less variable.

• Economic and Environmental Geology
• /
• v.46 no.2
• /
• pp.123-140
• /
• 2013

The Dangdu Pb-Zn deposit is located at approximately 10 km south of Jecheon, Korea. Geology of Dangdu deposit area consists of Pre-cambrian metamorphic rocks, Ordovician sedimentary rocks, Jurassic and Cretaceous igneous rocks. The ore deposit is developed along the fracture trending $N20{\sim}40^{\circ}W$ in Ordovician limestone and is considered to be a skarn type ore deposit. The shape of ore bodies developed in the Dangdu ore deposit can be divided into lens-form(two ore bodies of -30 m level adit and one ore body of -63 m level adit) and pocket-form developed in -30 m level adit. Ore minerals observed in the ore deposits are magnetite, pyrrhotite, pyrite, chalcopyrite, sphalerite, galena, cosalite, marcasite, hessite, native Bi and bismuthinite. Chemical composition of sphalerite ranges FeS 14.14~18.08 mole%, CdS 0.44~0.70 mole%, MnS 0.52~1.13, 1.53~2.09 mole%. Galena contains a small amount of silver with an average of 0.54 wt.%. An average composition of cosalite is Ag 2.43 wt.%, Bi 44.36 wt.%, Pb 35.05 wt.% which results the chemical formula of cosalite as $Pb_{1.7}Bi_{2.1}Ag_{0.2}S_5$. Skarn minerals consist of epidote, garnet, pyroxene, tremolite, quartz and calcite. The zoning pattern of the ore deposit can be subdivided into epidote-clinopyroxene zone, epidote-clinopyroxene-chlorite zone and epidote-garnet-clinopyroxene zone from the central part of the ore body towards the wall rocks. The chemical composition of garnet shows an increasing trend of grossular from epidote-clinopyroxene zone to epidote-garnet-clinopyroxene zone. Clinopyroxene occurs as a solid solution of diopside and hedenbergite, and the ratio of johannsenite increases from epidote-clinopyroxene zone to epidote-clinopyroxene-chlorite and epidote-garnet-clinopyroxene zones. The mineralization of the ore deposit is considered to be one stage event which can be separated into early skarn mineralization stage, middle ore mineralization stage and late low temperature mineralization stage. The temperature estimation from the low temperature mineralization range from $125{\sim}300^{\circ}C$ which is considered to be representing the temperature of late mineralization.