• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.214-233
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• 2002

Igneous rocks of Mt. Mudeung area are composed of Pre-Cambrian granite gneiss, Triassic hornblende-biotite granodiorite, Jurassic quartz diorite and Cretaceous igneous rocks. The Cretaceous igneous rocks consist of volcanic rocks (Hwasun andesite, Mudeung-san dacite and Dogok rhyolite) and granitic rocks (micrograpic granite and quartz porphyry). Major elements of the Cretaceous igneous rocks represent calc-alkaline rock series and correspond to a series of differentiated products from cogenetic magma. Igneous activity of Mt. Mudeung area started from volcanic activity, and continued to intrusive activity at end of the Cretaceous. In chondrite normalized REE pattern, most of igneous rocks of Mt. Mudeung area show similar pattern of Eu (-) anomaly. This is a characteristic feature of granite in continental margin by tectonic movement. Variation diagrams of total REE vs. La/Yb V vs. SiO$_2$ indicate differentiation and magnetite fractionation sequential trend of Hwasun andesite longrightarrowMudeungsan dacitelongrightarrowquartz porphyry. In mineral composition of these igneous rocks in mt. Mudeung area, composition of plagioclase and biotite coincidence with variation of whole rock composition, and emplacement and consolidation of magma is about 15 km (about 4.9 Kbar) in Jurassic quartz diorite and 2.0~3.2 km (0.6~1.0 Kbar) in Triassic hornblende-biotite granodiorite used by amphibolite geobarometer. Parental magma type of these granitic rocks of nt. Mudeung area corresponds to VAG field in Pearce diagram, and I-type in ACF diagram.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.197-207
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• 1997

Rocks in the Cheongsong mine area consist of Precambrian gneiss, Cretaceous sedimentry rocks and late Cretaceous quartz porphyry. The Cheongsong deposit is composed of many hydrothermal quartz veins of strikes $N30^{\circ}{\sim}60^{\circ}W$, dips $60{\sim}85^{\circ}E$ which fill WNW fault system. Pyrite and hematite occur within transparent quartz near margins of early stage II, and milky quartz of middle stage II coexists with sphalerite, chalcopyrite and galena coexisting with Cu-Pb-Bi minerals in center part of stage II quartz veins. Stage III calcite vein filled cracks or fractures of earlier quartz veins contains native copper and chalcopyrite. Supergene minerals are chalcocite, covellite, malanchite and chrysocolla. Alteration minerals are sericite, chlorite, argillite, epitode and pyrite. Ranges of salinities and homogenization temperatures for fluid inclusions in the individual periods of stage II are: 3.7 to 7.8 wt.% eq. NaCl and 200 to $380^{\circ}C$ in transparent quartz of early stage II; 0.7 to 6.4 wt.% eq. NaCl and 200 to $320^{\circ}C$ in milky quartz of middle stage II; 0.0 to 0.9 wt.% eq. NaCl and 250 to $320^{\circ}C$ in calcite of late stage II. Those of stage III calcite range about 0 wt.% eq. NaCl, and from 140 to $260^{\circ}C$, respectively. The relationship between salinities and temperatures shows decrease tendency with paragenetic time from stage II to III. The ${\delta}^{18}O_{H_2O}$ value is 0.5‰ in stage I, range from 0.5 to -0.4‰ in stage II, and from -3.2 to -3.7‰ in stage III. Calcite in the stage II and stage III has ${\delta}^{13}C$ values of -5.0‰ and -4.5 to -4.9‰, respectively. There is a decrease in sulfur fugacity values with paragenetic time of stage II, from $10^{-6.3}$ atm for early mineralization, to $10^{-6.5}$ atm for middle stage, to $10^{-8.0}$ atm for late mineralization of stage II. The results of stable isotope and fluid inclusion indicate that ore fluids reacted with meteoric water and wall rock in the Cheongsong hydrothermal system.

• Economic and Environmental Geology
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• v.3 no.4
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• pp.199-222
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• 1970

One of the biggest sulfide metallic (Cu, Pb, Zn) ore deposits of South Korea is located in the area of Seo-myeon, Shiheung-gun, Gyeonggi-do. Geology of the region is mostly composed of metasediments of biotite schist, graphite schist, injection gneiss, sericite schist, limesilicate and quartzite from bottom, those are applicable to so-called Yeoncheon System of Pre-Cambrian, and granodiorite, quartz porphyry, basic dykes are outcroped in a small scope as intrusives. The origin of the ore deposit is pyrometasomatic contact deposits due to hydrothermal replacement and the ore bodies are imbedded in lower bed of limesilicate formation as impregnation and ore minerals are galena, sphalerite, marmatite, chalcopyrite, bornite, chalcocite, covellite, and the later two minerals are both hypogene and supergene. Gangue minerals are mostly skarn minerals those hornblende, diopside, epidote, hedenbergite, chlorite, garnet and quartz except primary calcite and quartz. Boundary plane (NS strike) between schists and limesilicate seemed to be primary opening of ore solution and fractures bearing $N50^{\circ}{\sim}80^{\circ}W$ are secondary structural control for localization of ore minerals and the third structural controls are both irregular gashes and schistosity in small scale. Photogeological study was carried with vertical aerial photo scaled 1: 38,000 and enlarged 1 : 10,000 under stereoscope. The study on the area convinced the fact that the geologic boundaries between rocks, limesilicates and quartzites, are traced easily by their typical topographic feature and drainage, and the main fracture patterns which derived from the result of fracture traces, that photogeologic lineament observed under stereoscope, are those bearing (1) $N20^{\circ}W$, (2) $N58^{\circ}W$, (3) $N76^{\circ}W$, (4) EW, (5) $N20^{\circ}W$, (6) $N62^{\circ}W$, (7) $N77^{\circ}W$. Among the written fractures, (5) (not schistosity, in case of fault) (6) (7) are post-mineral faults and others are pre-mineral faults and others are pre-mineral structures, and (2) (3) (6) (7) are coincided with statistical figure of 208 fractures surveyed in underground. By the result of the study, mineralized zone, are presumed to extend north and southward, total length about 4km.

• Economic and Environmental Geology
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• v.23 no.3
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• pp.329-342
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• 1990

The purpose of this study is to clarify the nature of the differentiation and petrogenesis of igneous rocks in comparison with experimental results based on petrological and geochemical criteria. Study area is composed of the Precambrian granitic gneiss complex, Triassic meladiorite and biotite granodiorite, Jurassic biotite granite, and Cretaceous quartz porphyry. According to the data of EPMA, the clinopyroxene and orthopyroxene of meladiorite come under salite and hypersthene, respectively. Such results suggests that meladiorite is incipient differentiated products of basic magma under slow cooling condition. The petrochemical data of variation diagram of major element oxides vs. silica and of trace element oxide vs. silica, AMF triangle diagram and trace elements suggests that igneous rocks of study area are plutonic rocks belong to calc alkali rock series of the source of comagma intruded-emplaced in the order of meladiorite, biotite granodiorite and biotite granite by fractional crystallization of magma.

• Economic and Environmental Geology
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• v.11 no.2
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• pp.47-57
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• 1978

The study focused on the petrology and petrochemistry of the so called "Ganghwa syenitic rocks" which intruded into metasediment of basement in southeastern part of Ganghwa Island. The geologic sequence of the mapped area was shown in table 1, 10 model analyses and 7 chemical analyses on the rock samples taken from the Ganghwa syenitic rocks and Manisan granite have been used to discuss the nomenclature of the rocks and petrological relationship between rock types. The petrograpical and petrochemical features based on, the analyses are as follows: 1) Ganghwa syenitic rocks consist of Ganghwa alkali syenite and Ganghwa diorite porphyry which based on the classification of the subcommision on systematics of igneous of IGUS. Ganghwa diorite porphyry which occured as dike forms are intruded into Ganghwa alkali syenite. The rock forming minerals of Ganghwa alkali syenite are composed of perthite, plagioclase, quartz, hornblend and chlorite in major, and zircon, apatite, sericite and magnetite in minor. Ganghwa diorite porphyries consist of plagioclase, biotite, hornblend, orthoclase and chlorite, with, porphyritic texture. 2) In silica-oxides variation (Fig. 2) and AMF diagram (Fig_ 3), the Ganghwa alkali syenite is similar to the trend of Daly's average basalt-andesite-dacite-rhyolite than Skaergaard which shows the trend of the fractional crystallization of magma, and equivalent to the alkali rock series by Peacock. 3) The general trend of data points shift to plagioclase, and are superimposed on the alkali rich terminal part of the granodiorite province of SW Finland in normative Q-Kf-Pl(Fig. 4) and Or-Ab-An diagram respectively. The above-mentioned evidences suggested that the Ganghwa syenitic rocks are the differential products resulted by assimilation of intermediated magma and metasedment rock under relatively rapid cooling condition.

• Economic and Environmental Geology
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• v.2 no.1
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• pp.13-33
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• 1969

The Mulkum mine, located in Mulkum-myon, Yangsan-Kun, Kyeongsang Province, is one of the biggest iron mine in Korea. The geology of this mine and its vicinity consists of Chusan andesitic rocks and Datae-dong andesite porphyry of the Kyeongsang System which were intruded by biotite granite widely distributed near the vicinity of Mulkum-ni. The ore deposits, embedded in Dotae-dong andesite porphyry, are fissure-filling vein type in origin. Up to present ore bodies of Main vein, No. 2 vein, Eastern No. 1, 2 vein and Western No. 1 vein are exploited. Generally the veins strike N 10-25 E and dip to 60-90 SE. The proved length of vein is more than 500 meters and its depth 150 meters in Main vein with 3-4 meters of thickness in average. Ore minerals are mainly magnetite and locally associated with small amounts of hematite, sphecularite and chalcopyrite. Gangue minerals are quartz, epidote, chlorite, pyroxene, and garnet, etc. The modes of occurrence of vein are as follow; 1. Branching and parallel vein patterns are observed around main shaft in -1 level. 2. Multiple cymoid loops and subrectangular vein patterns are observed around main shaft in -2 level. 2. Single vein patterns are observed in -3 and -5 level. The ore-shoots plunge northeasterly about 20-30 degrees. In conclusion, the tectonically fractured zone belongs to the poorly mineralized zone and shoots are formed as single vein type. The general trends of one-shoots must be applied the prospecting of the deep-seated ore body in the deposits.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.571-577
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• 1995

Several acid-sulfate clay deposits associated with silicic magmas occur in the Haenam area of the southwestern part of Korea. Geology of the studied area consists of tuffs, granitic rocks, quartz porphyry, rhyolite, andesite and sedimentary rocks. The granitic rocks and quartz porphyry intruded tuffs and sedimentary rocks. The rhyolite and tuffs around the mines have undergone hydrothermally weak or strong alteration. Gold contents with major and trace elements have been determined for a total of sixty-seven specimens of fresh igneous rocks, wall rocks and minerals such as dickite and alunite by graphite furnace atomic absorption spectrometer and inductively coupled plasma. Gold is enriched in the alunite vein and the silicified zone, but is depleted in dickites and hydrothermally altered rocks with dickite of the Seongsan deposit. Gold is especially concentrated near the faults or conjunction area of two faults. High content of gold is shown in the mineral assemblages of alunitequartz- pyrite in the alunite vein and silicic zone of the Seongsan deposit compared with that of minerals and rocks from another deposits distributed in the studied area. Gold content in tuffs and dickites with pyrite is generally low. Gold content in silicified tuff tends to show positive correlations with content of As, Hg and Sb. Variation trends of Cd, Hg and Sb are similar to those of gold content. From the result of gold content variations, gold may be transported and concentrated by mineralizing solutions ascending along the cracks like fault. Therefore, it is important to survey alunite vein and silicified zone at the conjunction of faults, and to analyze pathfinder elements such as As, Hg and Sb for geological and geochemical exploration of gold in the studied deposits.

• 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.22 no.1
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• pp.17-20
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• 1989

Two rhyolitic rocks were taken at punggog of the Jangseong sheet in the Taebaegsan mineralized area and isotopically dated by K-Ar whole rock method. One is a rhyolite which gives $62.69{\pm}1.15Ma$ and the other is a rhyolitic tuff which gives $51.67{\pm}6.64Ma$, respectively. Generally K-Ar whole rock ages of the volcanic rocks can be assumed to be the formation age of them, if there is no geological criterion of secondary effects. But the two rhyolitic rocks were slightly hydrothermally altered and the age the rhyolitic tuff is a little younger than that of the rhyolite. However, there is no geological criterion to show any big hiatus between them in field, yet. Therefore, the age data would be interpreted, as that the rhyolitic rock mass has been probably extruded at about 60 Ma, a little older than 60 Ma, in the area. The ages of them probably appear to be secondary ages after the alteration. This fact well coincides with the K-Ar whole rock age of quartz-porphyry ($57.25{\pm}0.89Ma$) distributed near the 1st Yeonhwa Pb-Zn mine (Park et al., personal comm.), because the quartz-porphyry look to be a product of hydrothermal alteration of the volcanic rock.

• Economic and Environmental Geology
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• v.12 no.3
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• pp.147-176
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• 1979

The Yeonhwa II zinc-lead mine is characterized by a dozen of moderately dipping tabular orebodies of skarn and zinc-lead sulfides, developed in accordance with the ENE-trending bedding thrusts and bedding planes of the Pungchon Limestone and underlying Myobong Formation, mostly along the contacts of a ENE-trending sill and a NW-trending dike of quartz mononite porphyry. The orebodies occur in three groups: (1) the footwall Wolgok orebodies with respect to the sill, (2) the hangingwall Wolgok orebodies, and (3) the Seongok orebodies extended from dike contacts into carbonate beds. Mineral compositions of these orebodies are dominated by calc-silicates (skarn) associated with ore minerals of sphalerite, galena, and chalcopyrite, as well as sulfide gangue of pyrrhotite. A pair of exo- and endo-skerns in the Wolgok footwall contact aureole between the Pungchon Limestone and quartz monzonite porphyry on the -120 level represents a well-developed symmetrical pattern of mineral zoning: a garnet/quartz zone in the center of exoskarn, two zones of pyroxene with ore minerals on both sides of the garnet/quartz zone, further outwards-an epidote/chlorite-bearing hornfelsic zone in the Myobong slate beyond a zone of unaffected limestone, and an epidote-dominated zone of endo skarn on the opposite side toward fresh quartz monzonite porphyry. These features indicate a combination of two effects on the skarn formation: (1) differences in composition of the host rocks(sedimentary and ignous), and (2) progressive outward migration of inner zones on outer zones on the course of metasomatic replacement of the pre-existing minerals. Microprobe analyses of garnet, pyroxene, pyroxenoids, epidote, and chlorite for nine major elements on a total of 23 mineral grains revealed that: the pyroxenes are hedenbergitic, in most zones, with a gradual decrease of Fe- and Mn-contents toward the central zone, whereas the garnets are andraditic in outer zones, but are grossularitic in the central zone. This indicates a reverse relationship of Fe-contents between pyroxene and garnet across the exoskarn zones. Pyroxenoids are lacking in wollastonite but are dominated by pyroxmangite, rhodonite and bustamite, indicating a Mn-rich nature in bulk chemistry. Pseudomorphic fluorite after garnet occurs abundantly reflecting a fluorine-enhanced evidence of the skarn-forming fluids. Epidote contains 0.19-0.25mole fraction of pistacite, and chlorite is Mn-rich but is Mg-poor. Sulfide mineralization took place with the most Fe-rich pyroxene rather than with garnet as indicated by the fact that the highest value of hedenbergite mole fraction occurs in the ore-bearing pyroxene zone. The Yeonhwa II ores are characterized by high zinc and low lead in metal grade, with minor quantity of copper content in almost constant grade. The hangingwall Wolgok and Seongok orebodies, that formed in a more open environment with respect to their local configurations of geologic setting, are more variable in metal grades and ratios, than are the footwall Wolgok orebodies formed in a more closed condition in a narrow interval of sedimentary beds.