• 자원환경지질
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• 제10권4호
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• pp.177-184
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• 1977

This study is focused on the geological structure of Igog-Jangam folded zone in the vicinity of Goesan town where Ogcheon group distributes. The geology is composed of Gyemyungsan formation, Daehyangsan quartzite, Munjuri formation and Hwanggangri formation of Ogcheon group unknown age in descending order, and porphyritic biotite granite and dyke rocks that intruded into the Ogcheon group. The study revealed that Igog-Jangam folded zone is a plunged synclinal fold based on the following evidences; 1) Some pebbles in Hwanggangri formation at Minaemi-gol (a name of village) consists of phyllite of Munjuri formation. 2) The pebble bearing phyllitic bed in this area, Hwanggangri formation was recognized as the uppermost member in Ogcheon group instead of the basal one of the group. 3) A crest of anticlinal fold has been appeared near the Goegang bridge as a structural counter-part of that of the present area. 4) The study of lineation of minor fold in Munjuri formation also suggests that Igog-Jangam folded zone manifests to be a synclinal structure.

• 자원환경지질
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• 제13권2호
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• pp.91-103
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• 1980

In spite of the fact that the Okcheon system has been rather intensively studied by many geologists since 1945, it still remains as a controversal problem as to its stratigraphy and geologic age. Present study has mainly focused on the upper members of the Okcheon system, namely the Hwanggangri and the Kunjasan formations so as to clarify the lithology, the depositional environment and the tectonic evolution of the formations. The Kunjasan formation lying unconformably over the Hwanggangri formation which is supposed to be a meta-tillite is interpreted as a metamorphosed calcareous argillaceous and/or arenaceous sediments on contract to the idea postulated by some geologists that it was a derivative of silicified Hwanggangri formation. Lithology of the Kunjasan and the Hwanggangri formation is quite different in that the former is white in color, contains few pebbles, and mostly composed of diopside and detrital quartz, whereas the latter is black to dark in color, contains abundant and variable kinds of pebbles, and composed of more argillacous matrix that has been metamorphosed to hornfels. The Hwanggangri and the Kunjasan formations were deposited in the rather deep sea which has transgressed toward northeast from southwest in the late Precambrian time, and the writer (1970) had formerly designated it as Okcheon Paleogeosyncline. With the beginning of Paleozoic era, Okcheon neogeogyncline was formed to the northeast of the old paleogeogyncline area. The transgression of the sea had proceeded toward southwest in which Cambrian strata were accumulated. During this period the area occupied formerly by the paleogeosyncline was uplifted, so that most of the Hwanggangri and the Kunjasan formations were eroded away except in the area close to the neogeosyncline sea coast. This is the reason why the Hwanggangri and the Kunjasan formations are cropped out presently in the area of the vicinity of contact zone of the paleo- and neogeosyncline zones. The age of the Okcheon system has been reconfirmed to be Precambrian from the view of the facts that 1) the Hanggangri formation, the upper member of the Okcheon system is meta-tillite and correlated to the Precambrian tillite in the Yantze basin in China, 2) the Okcheon system has been moderately metamorphosed while other formations of the same age, if it is Paleozoic or later, have not been metamorphosed, and 3) tectonic history and limited areal distribution of the Hwanggangri and the Kunjasan formations is suggestive of Precambian age.

• 자원환경지질
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• 제10권1호
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• pp.19-35
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• 1977

The study area is located in between Hacheonri and Weolgulri, Jecheon-gun where the formations of Okcheon group and Chosun group come in contact and the stratigraphy and geological age of the Okcheon group have been debated among previous workers. The dolomitic limestone which distributed at Cheongam and Dumusil is clarified as the Hyangsanri dolomite formation and the quartzite distributed at Cheongam and Howeunri as Taehyangsan quartzite formation. The newly named Soorumsan schist interbedded in the Great Limestone Series was previously classified Seochangri formation. It is also classified that the formation formerly named as Seochangri was divided into newly named Manji schist which seems to be correlated to Kemyeongsan and Munjuri formation. The formation formerly named as Buknori is clarified as Hwanggangri formation. The Samtaesan formation has been clarified as the lower and upper limestone beds which belong to the Great Limestone Series. The area divided into two groups, that is, Okcheon system of Pre-cambrian age occupies western part and the Great Limestone Series of Chosun system of Cambro-Ordovician age eastern part of this area. Okcheon system consists in ascending order of Manji schist, Hyangsanri dolomite, Taehyangsan quartzite, Munjuri schist, and Hwanggangri formation of meta-tillite. The Great Limestone Series of Chosun group consists in ascending order of lower limestone, Soorumsan schist, Hoosanri quartzite and upper limestone formations. Busan augen gneiss seems to be igneous origin. Unmetamorphosed shale interbed can be traced in the Soorumsan schist. Previous study (Kims, 1974) reveals that meta-volcanic rocks are distributed from south to north along contact zone of the Okcheon and Chosun groups, and it has been confirmed that the meta-volcanics crop out continuously from the adjacent southern quardrangle into the southern part of the area studied, intruding along the fault zone between the Okcheon and Chosun groups which seems to be upthrust as in the area south. This evidence coincides with Kims' work (1974) which states that the Precambrian Okcheon group is largely overturned and thrusted over the Chosun group.

• 자원환경지질
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• 제7권3호
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• pp.101-122
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• 1974

The study area is located in between Susanri and Hwanggangri where the formations of Okcheon group and Chosun group supposedly come in contact so that the area is structurally very import. Present study reveals that the meta-volcanic rocks distribute from south to north along contact zone of Okcheon and Chosun groups in the center of the area. Meta-volcanic rocks seem to be originated from the andesite or andesitic basalt rocks which was known to be Surchangri formation consist of phyllite and black slate by previous workers. The meta-volcanic rocks intruded along the fault zone one existed between Okcheon and Chosun groups but obliterated at present by the intrusion of volcanic rocks. The fault seems to be overthrust, and one of the positive evidences of thrust fault is the Yamisan nappe structure in Yamisan near Susanri. This interpretation coincides with O.J. Kim's work which states that the Precambrian Okcheon group is largely overturned and thrusted over the Chosun group. The relation between the Surchangri and the Majeonri formation marks facies change. This fact together with northpluging anticlinal structure made it possible that both formation came into contact along direction without fault. Yongam formation is not overlain unconformably used to be believed by previous workers, but interbed in the Great Limestone series of Chosun goup. It is also clarified that the rock formerly designated as limesilicate rock was meta-liparite. The origin of amphibole pebbles in the Kunjasan formation is of primary and secondary ones; the secondary pebbles were formed by metamorphism of the fragments of limestone or dolomite.

• 자원환경지질
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• 제29권1호
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• pp.25-33
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• 1996

Stable isotopic ratios of the carbonate rocks and chemical compositions of the matrix of pebble bearing phyllitic rocks known as the Hwanggangri Formation, which are in hot debate on their origin such as tillite, debris flow and turbidite, were determined to interpret their depositional environment. Argillaceous matrix of the pebble bearing phyllitic rocks has a high content of CaO (av. 19.5%) and MgO (av. 8.3%), corresponding to calcareous sandy shale. No difference of chemical compositions including trace elements and REE is in the matrices between the Hwanggangri and the Kunjasan Formations. Carbonate rocks from the Okchon zone and outside of the zone range $-2.5{\sim}+6.1$‰ in ${\delta}^{13}C$ and $+5.8{\sim}+25.9$‰ in ${\delta}^{18}O$, indicating normal marine limestone. However, unusally $^{13}C$ enriched carbonate rocks might be deposited in the highly evaporated sedimentary basin. A wide variation of ${\delta}^{18}O$ values is responsible for metamorphism with a $^{18}O$ depleted meteoric water. Isotopic equilibrium temperatures by graphite-calcite geothermometer show a higher metamorphic temperature ($547{\sim}589^{\circ}C$) in the Okchon zone than those ($265{\sim}292^{\circ}C$) in the Samtaesan Formation of the Chosun group. Rhythmic alternation of relatively thin shale with thin limestone in the Kounri Formation is not cherty layer but thin limesilicate bed by metasomatic replacement. Judging from the isotopic and chemical compositions of the carbonate rocks and calcareous matrix of the pebble bearing phyllitic rocks, the Hwangganari Formation was deposited in the shallow marine environment favorable to debris flow.

• 자원환경지질
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• 제34권1호
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• pp.133-146
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• 2001

옥천대 중부 충주-수안보 일원에 분포하는 황강리층을 대상으로 대자율 비등방성을 측정하고 야외 지질구조 자료들을 수입하였다. 그 결과, 연구지역의 북동부와 남서부 지역은 변성과 변형사가 서로 달랐음이 드러났다. 황강리층에는 야외에서 구별되는 두 종류의 벽개, 즉 점판벽개($S_1$)와 파랑벽개($S_2$)가 발달하고 있으나 $S_1$면은 연구지역의 북동부에서 뚜렷이 관찰되는 반면, 남서부에서는 $S_2$면의 발달이 절대적으로 우세하다. 등온잔류자기 강도, 제적 총 대자율 그리고 비등방성의 정도는 모두 남서부에 비해 북동부 지역에서 훨씬 높은 값을 보이고 있으며 남서쪽으로 갈수록 이들 값들이 현저히 감소하여 남서부 지역에 이르러서는 일관되게 매우 낮은 값을 보여준다. 또한, 대자율 비등방체의 형태도 북동부 지역에서 자기적 엽리구조가 우세하며 남서쪽으로 갈수록 선구조 영역으로 점진적으로 변화되어 남서부 지역에 이르러서는 일관되게 구에 가까운 형태를 이룬다. 이러한 사실들은 모두 북동부에 비해 남서부에서 보다 강한 후기 변성과 변형이 있었음을 지시하는 것이다. 한편, 북동부 지역에서 얻어진 대자율 비등방 타원체의 주축들($k_1$, $k_2$, $k_3$)의 분포 양상을 근거하면, 연구지역 황강리층은 세 번의 변형사건($D_1$, $D_2$, $D_3$)을 겪은 것으로 해석된다. 북서-남동방향의 압축력에 의해서 북동-남서방향의 $S_1$면이 형성되고 이 엽리면을 따라 순수 전단작용이 발생하여 황강리층을 편평화시킨 동축 변형사건($D_1$)이 제일 먼저 있었으며, 이후 $S_2$면을 따라 북서향의 충상단층과 좌수향의 연성 혹은 준 연성의 단순 전단작용이 일어나 기존의 변형타원체의 주축들이 차별적으로 회전되는 비동축 변형사건($D_2$)이 있었고, 마지막으로는 북동방향의 수평축을 가진 요굴습곡을 형성시킨 변형사건($D_3$)이 있었다. 남서부 지역에서는 비등방 타원체의 모든 주축들이 분산되어 있으며 야외에서 $S_2$면이 우세하게 관찰되고 북동부에 비해 IRM강도, 체적 총대자율 그리고 대자율 비등방성 정도 등이 한결같이 매우 낮다. 이러한 점들은 북동부에 비해 강한 후기 변형 혹은 변성 과정에서 자성광물의 배열이 분산되었거나 강한 $D_2$변형으로 $D_1$변형타원체가 중첩되어 역변형된 결과이거나 혹은 이 두가지가 복합된 결과로 해석된다.

• 자원환경지질
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• 제14권2호
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• pp.55-76
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• 1981

Southwestern contact zone of the Boeun granodiorite occurs near the thrust fault between the Ogcheon Group and Majeonri Limestone Formation. Ogcheon Group, metasediments composed of the Munjuri Formation, Changri Formation, and unconformably overlying Hwanggangri Formation, belongs to greenschist facies of regional metamorphism accompanied with deformation of two fold axes, $N10^{\circ}E$ and $N45-65^{\circ}E$ directions. Basic metamorphic rocks occurring in the Changri and Limestone Formations are the meta-basalts and meta-diabases of tholeiitic basalt series. The meta-basalts intruded in the Changri Formation as sills, whereas the meta-diabases in the Changri and Limestone Formations as stocks in appearance. They are considered to have emplaced before the formation of two fold axes and related with the thrust fault, based on the geologic setting of the area. The metamorphic facies are identified to be greenschist facies to epidote-amphibolite facies for the meta-basalt, and epidote-amphibolite facies for the meta-diabases. It is interpreted that such a variety of facies was related from the combination of earlier deuteric alteration and later regional metamorphism. The metasediments in southwestern contact zont of the Boeun granodiorite which is a product of later syntectonic intrusion of middle Jurassic in age, show pyroxene-hornfels facies near the contact and amphibole-horenfels facies away from the contact to the mineral zoning in the contact metamorphic aureole of the Limestone Formation, based on the paragenetic analysis of mineral assemblages. The Limestone in the area appears to be considerably $SiO_2-CaO-MgO-CO_2-H_2O$ can be adopted to evaluate equilibrium conditions of the mineral assemblages in each mineral zone. It is revealed that a temperature gradient was existed accross the contact aureole ranging from the higher igneous side to lower sedimentary side, whereas no clear trend of $XCO_2$ variation appears but high mole fraction. The tremolite diopside-quartz-calcite assemblages occurs in common through the most mineral zones of contact aureole that is in good agreement with the equivalent reaction curve which extends over a wide range of $T-XCO_2$ conditions.

• 자원환경지질
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• 제11권4호
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• pp.169-182
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• 1978

The Weolagsan area consists of four units; (1) Low grade meta-sediments of the upper members of Ogcheon age unknown group such as Changri (mainly black slate and phyllitic rock), Majeonri (mainly alternation of slate, limestone and chert) and Hwanggangri Formation (pebble bearing phyllitic sediments); (2) Samtaesan Formation of Chosun System of Ordovician; (3) So called meta-volcanics and (4) Weolagsan Granite and its associations which intruded above mentioned meta-sediments and meta-volcanics. This study was focused to know the Woelagsan granite and its metasomatic effects to the country rocks petrographically and petrochemically. According to the field survey, microscopic work and some chemical analysis, the granite is a "normal granite" based on the Streckeisen's classification and belongs to a mass of the Central-zone younger group in Ogcheon geosynclinal belt. The granite metasomatized the country rocks along its northern contact zone. Zone of calcareous and cherty rocks (Majeonri formation) was silicified partly and skarned locally at the contact with the granite. The chemical analysis of the zone show no difinite variations in contents of $SiO_2$ and CaO with the distance from the granite. It seems to be indicated that the silicification of this part was not so metasomatized by the granite body, but thermally affected as much as to be partially remelted in the specific parts of the formations. Meta-volcanic rock zone was slightly chloritized near contact with the granite. Limestone of Samtaesan Formation was silicified and skarned along the contact zone by the granite body. The chemical analysis of the zone show some noticiable changes in compositions of $SiO_2$ and CaO with distance from the granite boundary. It can be imagined that the silicification of this zone was metasomatically originated by Woelagsan Granite. According to chemical analysis on several trace elements, the ratio of Zn/Cr and Ni/Cr are relatively higher than that of Cu/Cr in the above mentioned silicified zones. Generally the variation of these metal elements in the zones tend to be regular with distance from the granite body.

• 자원환경지질
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• 제13권4호
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• pp.215-227
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• 1980

The rock units of Goesan area in the Ogcheon metamor phic terrain established on the basis of field criteria should be redefined into following sequence. Based on shear senses in secondary small structures which are usually observable in the investigated area, the stratigraphy can be lithologically divided into the lower pelite, pebbly mudstone, upper pelite, quartzite and psammite unit in ascending order. This conclusion is in discordance with a previous opinion; Munjuri formation and Guryongsan formation may be equivalent to upper pelite unit, Iwonri formation and Hwanggangri formation to pebbly mudstone. From this, it may be inferred that isoclinal overturned folds repeatly occur in the area. The uranium bearing coaly thin layers in upper pelite unit have relatively broad exposures in Deogpyeongri block of Goesan area along culmination zone in the central part of the investigated area. It is believed that structural feature in the block recognized complexly refolded synform plunging to southwest. Mineralogical and radiometric studies were made on 135 representative samples from the Ogcheon Group of Korea. The mineralogy of all black slate samples is qualitatively similar but quantitatively ·different. The uranium distribution in the studied area show approximately log normal. Uranium in the black slates of the Ogcheon Group was deposited together under same physico-chemical environmental conditions. The chemical and geological factors that controlled the abundance of organic carbon and iron oxides also controlled the uranium content. The relationship of the major components to uranium can be expressed by the following regression equation: $Log(U\times10^4+1)$= 1.70999-0.00367(quartz)0.00512(micas)-0.00930 (other silicates)+0.01911 (iron oxides)-0.03389(other opaques)+0.02062(organic carbon).

• 자원환경지질
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• 제22권3호
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• pp.237-252
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• 1989

The Inseong gold-silver mine is located 3Km northwest of Suanbo, Choongcheongbugdo, Republic of Korea. The mine occurs in the shear zone formed by tension fractures within the Hwanggangri Formation of the Ogcheon metamorphic belt. Ore minerals found in the gold-silver bearing hydrothermal quartz vein composed mainly of pyrite, arsenopyrite, sphalerite, galena and minor amount of chalcopyrite, pyrrhotite, stannite, bismuthininte, native bismuth, chalcocite, electrum and tellurian canfieldite(?). The gangue minerals are quartz, calcite, chlorite and rhodochrocite. Wallrock alterations such as chloritization, silicitication, pyritization, carbonitization and sericitization can be observed in or around the quartz vein. According to the paragenetic sequence, quartz vein structure and mineral assemnlages, three different stages of ore formation can be recognized. The physico-chemical environment of ore formation in this deposit shows slight variation from stage to stage, but the condition of main ore deposition can be summarized as follows. Fluid inclusion, S-istope geothermometry and geothermometry based on mineral chemistry by use of arsenopyrite and chlorite show the ore was formed at temperature between 399 and $210^{\circ}C$ from fluids with salinities of 3.3-5.8 wt.% equivalent NaCl. It indicates that pressure during the mineralization is less than 0.6 Kb corresponding to a depth not greater than 1Km. S-isotope data suggests that thermal fluid may have magmatic origin wit some degree of mixing with meteoric water. In coclusion, the Inseong gold-silver deposit was formed at shallow depth and relatively high-temperature possibly with steep geothermal gradient under xenothermal condition.