• Economic and Environmental Geology
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• v.21 no.3
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• pp.319-329
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• 1988

As a factor which can help to understand the genesis of (mata) sedimentary and/or hydrothermal uranium depisits, an interpretation of the role of organic matter associated with uranium mineralization, was attempted with the literature published up to the end of 1986. Laboratory studies, in which diageneis and metamorphism are artificially simulated, can help to elucidate how uranium with particular organic materials are formed and destroyed. Similarly, research involving a variety of techniques is needed to characterize both the soluble organic extracts (bitumen) and the insoluble organic matter (kerogen), separated from uranium ores and associated rocks. In the presence of clay minerals and amorphous oxy-hydroxde minerals, an understanding of the role of organic matter must be prudent and may require the incorporation of multidisciplinary approach (mineralogy, inorganic geochemistry ...).

• The Journal of the Petrological Society of Korea
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• v.3 no.3
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• pp.196-219
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• 1994

Granulite complexes in northern (the Nangnim block), eastern (ther Kimchaek zone of the Macheonryong belt) and southern (separate windows among upper Proterozoic structure such as the Wonsan, Nampo and Haeju granulites) parts of the Northern Korea are studied. Multistage deformations, metamorphic and migmatitic events, and granite formations are recognized in these granulite complexes. Mineral thermobarometry and fluid inclusion investigationss are used to establish the P-T evolutionary trends during prograde and retrograde metamorphic events. The peak metamorphism of granulites is characterized by temperature near $800^{\circ}C$ and pressure near 5.5-6 kb. Retrograde evolution includes cooling at constant pressure or with variable pressure ranging up to 7-8 kb. This P-T change corresponds to the transition from high to moderate or low geothermal gradient. The subsequent cooling is ac-companied by significant decompression to 3-4 kb.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.129-150
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• 2012

The tectonic evolution of the Central Ogcheon Belt has been newly analyzed in this paper from the detailed geological maps by lithofacies classification, the development processes of geological structures, microstructures, and the time-relationship between deformation and metamorphism in the Ogcheon, Cheongsan, Mungyeong Buunnyeong, Busan areas, Korea and the fossil and radiometric age data of the Ogcheon Supergroup(OSG). The 1st tectonic phase($D^*$) is marked by the rifting of the original Gyeonggi Massif into North Gyeonggi Massif(present Gyeonggi Massif) and South Gyeonggi Massif (Bakdallyeong and Busan gneiss complexes). The Joseon Supergroup(JSG) and the lower unit(quartzose psammitic, pelitic, calcareous and basic rocks) of OSG were deposited in the Ogcheon rift basin during Early Paleozoic time, and the Pyeongan Supergroup(PSG) and its upper unit(conglomerate and pelitic rocks and acidic rocks) appeared in Late Paleozoic time. The 2nd tectonic phase(Ogcheon-Cheongsan phase/Songnim orogeny: D1), which occurred during Late Permian-Middle Triassic age, is characterized by the closing of Ogcheon rift basin(= the coupling of the North and South Gyeonggi Massifs) in the earlier phase(Ogcheon subphase: D1a), and by the coupling of South China block(Gyeonggi Massif and Ogcheon Zone) and North China block(Yeongnam Massif and Taebaksan Zone) in the later phase(Cheongsan subphase: D1b). At the earlier stage of D1a occurred the M1 medium-pressure type metamorphism of OSG related to the growth of coarse biotites, garnets, staurolites. At its later stage, the medium-pressure type metamorphic rocks were exhumed as some nappes with SE-vergence, and the giant-scale sheath fold, regional foliation, stretching lineation were formed in the OSG. At the D1b subphase which occurs under (N)NE-(S)SW compression, the thrusts with NNE- or/and SSW-vergence were formed in the front and rear parts of couple, and the NNE-trending Cheongsan shear zone of dextral strike-slip and the NNE-trending upright folds of the JSG and PSG were also formed in its flank part, and Daedong basin was built in Korean Peninsula. After that, Daedong Group(DG) of the Late Triassic-Early Jurassic was deposited. The 3rd tectonic phase(Honam phase/Daebo orogeny: D2) occurred by the transpression tectonics of NNE-trending Honam dextral strike-slip shearing in Early~Late Jurassic time, and formed the asymmetric crenulated fold in the OSG and the NNE-trending recumbent folds in the JSG and PSG and the thrust faults with ESE-vergence in which pre-Late Triassic Supergroups override DG. The M2 contact metamorphism of andalusite-sillimanite type by the intrusion of Daebo granitoids occurred at the D2 intertectonic phase of Middle Jurassic age. The 4th tectonic phase(Cheongmari phase: D3) occurred under the N-S compression at Early Cretaceous time, and formed the pull-apart Cretaceous sedimentary basins accompanying the NNE-trending sinistral strike-slip shearing. The M3 retrograde metamorphism of OSG associated with the crystallization of chlorite porphyroblasts mainly occurred after the D2. After the D3, the sinistral displacement(Geumgang phase: D4) occurred along the Geumgang fault accompanied with the giant-scale Geumgang drag fold with its parasitic kink folds in the Ogcheon area. These folds are intruded by acidic dykes of Late Cretaceous age.

• The Journal of the Petrological Society of Korea
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• v.19 no.2
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• pp.157-165
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• 2010

The age unknown Ogcheon metasedimentary rocks and the Jurassic Ogcheon granite (Jocgr) intruding it are distributed in the Ogcheon area, which is located in the central part of the Ogcheon Belt, Korea, This paper newly examines the timing of Honam shearing on the basis of the microstructural researches on time-relationship between the crenulation of Ogcheon metasedimentary rocks and the contact metamorphism by the intrusion of Jocgr. The D2 crenulation phase, which is defined by the microfolding of the S1 foliation in the metasedimentary rocks, is divided into two sub-phases. The one is a sub-phase of Early crenulation (D2a) which is included within old andalusite porphyroblasts, and the other is that of Late crenulation (D2b) which warps around the old andalusite. But they show the same dextral shear sense, the axial planes parallel to each other, and a single crenulation at outcrop scale. The contact metamorphism of andalusite-sillimanite type by the Jocgr occurred during the inter-phases of D2a and D2b, and crystallized the old andalusite masking the D2a crenulation and fibrous sillimanites replacing the D2a crenulation-forming muscovites. New andalusite porphyroblasts synkinematically grew in pressure shadows around the old andalusite or in its outermost mantles during the early stage of the D2b. The D2b occurred still continuously after the growth of the andalusite ceased (= later stage of the D2b). It indicates that the D2b occurred continuously during the period when the Ogcheon granite was still hot and cool. From this study, the crenulation history of Ogcheon metasedimentary rocks and the timing of Honam shearing would be newly established and reviewed as follows. (1) Early Honam shearing; formative period of Early crenulation, (2) main magmatic period of Jurassic granitoids; growth of the old andalusite and fibrous sillimanite by the intrusion of Jocgr, (3) main cooling period of Jurassic granitoids; formative period of Late crenulation related to Late Honam shearing, growth of the new andalusite in the early stage of D2b. Thus, this study proposes that the Honam shear movement would occur two times at least before and after the intertectonic phase which corresponds to the main magmatic period of Jurassic granitoids.

• Economic and Environmental Geology
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• v.34 no.4
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• pp.395-415
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• 2001

In the Singok area, western part of Chungcheongnam-Do, two ultramafic ma~ses, Singok mass and Kaewol mass, occur as isolated lenticular bodies in the Precambrian Kyeonggi gneiss complex. The masses extend for several hundred meter to NNE direction, parallel to the main fault line of this area. The rocks are dunite and harzburgite, but partially and absolutely serpentinized. They dominantly show porphyroclastic and recrystallized textures with equigranular-mosaic and protogranular textures. In spite of differences among the alteration and metamorphism, the ultramafic masses are characterized by varying amounts of high fosteritic olivine ($Fo_{0.88-0.93}$), magnesian pyroxene ($En_{0.93-0.97}$), and tremolitic to tschermakitic hornblende with minor spinel, serpentine, chlorite, calcite, magnetite, phlogopite and talc. It is compared with adjacent gneiss complex containing amphibole, biotite, plagioclase, alkali-feldspar and quartz. Geochemically, these rocks show high magnesium number (Mg>90.38), and transitional element (Ni=595-2480, Cr==IOlO-4400, Co=36-120 ppm), low alkali element ($Na_{2}O$<0.3, $K_{2}O$<0.11, $Al_{2}O_3$<2.95 wt%) and depleted incompatible element contents, which is compared with adjacent rocks (Mg < 83.69, $Na_{2}O$=1.02-3.42 wt%, $K_{2}O$=O.67-5.65 wt%, $Al_{2}O_3$=9.15-16.86 wt%, Ni < 435 ppm, Cr < 1440 ppm, Co<59 ppm, enriched incompatible element contents). Overall characteristics of ultramafic rocks from the Singok and Kaewol masses are similar to the those of adjacent ultramafic bodies in Chungnam with worldwide orogenic related Alpine type ultramalic rocks. Calculated geothermometries suggest that the ultramafic rocks have experienced metamorphism in the condition ranging from the greenschist facies to granulite facies.

• The Journal of the Petrological Society of Korea
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• v.9 no.4
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• pp.211-237
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• 2000

Major element zoning has been analyzed in garnet porphroblasts obtained from the Grt-St and Ky-Grt-St grade assemblages in Zones I on the northern flank of the Pelham Dome, north central Massachusetts. These porphyroblasts grew during multiple phases of deformation and meta-morphism revealed by the inclusion trail geometry plus the chemical zoning patterns within garnet porphyroblasts. Unusual zoning patterns, including zoning reversals and gradient changes in XMn, zlgzag patterns in Fe/(Fe +Mg) and staircase-shaped patterns in XCa, are coincident with textural truncations and other changes in microstructure within the garnet porphrublasts. Chemical variations in plagioclase, biotite, muscovite and staurolite combined with inclusion trail geometry and petrography reveal that the garnet zoning patterns are modified by combinations of the following. (1) Uni-and divariant reactions involving garnet consumption(Grt+ Chl+Ms=St+Bt+Qtz + $H_2$O) and production(St+Ms + Qtz= Bt+ Grt +A1$_2$$SiO_{5}$ + $H_2$O). (2) Deformation induced episudic ionit dissolution, preferential diffusion and re-distribution during foliation development. (3) P-T changes during growth of the porphyroblasts. The P-T paths combined with petrographic and inclusion trail morphology observations consist of two pattens; (1) heating/compression during NW-SE shortening; and (2) decompression with cooling during NNW-SSE shortening. Based on temperature-time(T-t) geochronological data and late-Paleozoic tectonic model, Alleghanian metamorphism, which is the result of heterogeneous shearing concentrated along the boundary between the Abalone Terrane(Pelham dome) and cover rocks(Bronson Hill Terrane), has produced Ky-St-Ms mineral assemblage during Pennsylvanian(290-300 Ma) in Shutesbury area. However, temperature of alleghanian metamorphism was not high enough to form garnet and staurolite in the Northfiled syncline area. Alleghanian metamorphism has affected only the matrix due to heterogeneous shearing in the study area.

• The Journal of the Petrological Society of Korea
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• v.6 no.2
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• pp.77-85
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• 1997

The Early Proterozoic reworked rock association occurs within the Preacmbrian high grade metamorphic rocks in the area of Daqingshan, Inner Molgolia. In this association, the various large scale ductile deformation belts, form a nappe structure where the foliation steeply dips to north and the lineation ($340^{circ}-30^{\circ}$) plunges at $45^{\circ}55^{\circ}$. This result indicates the subduction/extension with northern part thrusting over the southern part at high angle. The southern subducted microlithon has the characteristics of prograde metamorphism. The northern thrusted microlithon shows the evidence of retrograde metamorphism with decreasing pressure and increasing temperature. The main rock types of Early Proterozoic Moyites are biotite adamellite and syenogranites occurring in the form of small batholiths or stocks and alkali-feldspar granites in veins. The biotite adamellites are progressively contacted with the Archean and Early Proterozoic rocks and contain a great deal of enclaves of metamorphosed rocks, suggesting an anatexis origin. The geochemical characteristics of moyites show the typical features of anatexis granite. At middle to late Early Proterozoic time, the continent-continent collision formed the large scale thrusting and imbrication of Archean basement rocks. According to the mineral assemblage and thermobarometer of Paria et al. (1988) give the following P-T condition : up-faulted block; $700-710^{\circ}C$, 0.72-0.78 Gpa (early stage) and $600^{\circ}C$, 0.44 Gpa (late stage), footwall block; $620^{\circ}C$, 0.8 Gpa (early stage), $620-840^{\circ}C$, 0.64-0.45 Gpa (peak) and $620-630^{\circ}C$, 0.35Gpa (late stage). These results suggest a clockwise P-T-t path (jin et al., 1991, 1994). According to the depth-temperature model in the comperature subduction zone and the experimental data of Wyllie et al. (1983), we propose a tectonic-magmatic-thermal model to account for metamorphism-anatexis of moyite occurring in subduction-shear zone.

• Economic and Environmental Geology
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• v.15 no.2
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• pp.89-102
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• 1982

Several mines in Jeonnam produce the ores of having high SK number of refractoriness. Among those for 5 mines, this paper deals with the relationahip between SK number and mineral composition of the ore, and with the genesis of the deposits. 1. Byok-Song and Chon-Un Mine: Mineral compositions of the ores are chiastolite, chloritoid(monoclinic), kaolinite, sericite, diaspore, corundum, and quartz. The ores having SK number of 36 or 37, consist chiefly of chiastolite and diaspore and a little amount of kaolinite, sericite, corundum, chloritoid, and quartz. The ores having SK number of 33 or 34 consist of chloritoid, sericite, kaolinite, chiastolite, and diaspore. With increasing the amount of chloritoid and sericite, and decreasing the amount of diaspore and chiastolite, the SK number of the ores decreases. The deposit, originally high alumina-bearing shale of Chon-Un San formation, seems to be formed by contact metamorphism(forming of chiastolite), regional metamorphism(forming of monoclinic chloritoid), and hydrothermal replacement(forming of large crystal of diaspore veinlets). 2. Song-Sauk Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz and a little amount of kaolinite, dickite, diaspore, and pyrite. Many spherical inclusions containing in pyrophyllite deposits, consist chiefly of diaspore and kaolinite, The inclusions have the high SK number of 38. Amount of spherical inclusions is about 5 % to the whole pyrophyllite ores. The SK number of other pyrophyllite ore is less than 32. Quartz and pyrite are chief minerals lowering the SK number of the ore. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff of Mesozoic age. Spherical inclusions consisting of diaspore and kaolinite, show the selective replacement of hydrothermal solutions to the materials of feldspar in tuff. 3. Seung-San Mine: Mineral compositions of the ores are chiefly kaolinite, dickite, diaspore, and quartz. But some part of the mine consists of alunite deposits. The ores having SK number of 35 or higher consist chiefly of kaolinite and diaspore and a little amount of quartz. With increasing the amount of quartz and decresing the amount of diaspore, the SK number of the ore decreases. The deposits have been formed by hydrothermal processes by replacing the siliceous tuff and quartz porphyry. 4. Wan-Do Mine: Mineral compositions of the ores are chiefly pyrophyllite and quartz. But some ore contains a little amount of diaspore, kaolinite, pyrite, and chloritoid. The ores having high SK number of 36 consist chiefly of diaspore and pyrophyllite. Pyrophyllite ore has a SK number of 32 or lower. Amount of quartz and pyrite decreases the SK number of ores in this mine. Rhyolite was replaced by the action of hydrothermal solutions forming the pyrophyllite deposits.

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.25-35
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• 2014

The sedimentary rocks exposed around Mt. Palgong were subjected to metamorphism due to a granitic magma intrusion at late Cretaceous, and they eventually metamorphosed to hornfels by the action of both hydrothermal solution and high temperature supplied from the magma. The hornfels zone around the granite body ranges from 2.0 to 3.5 km in width but the boundary between hornfels and sedimentary rocks is not obviously defined because the metamorphic grade gradually decreases with distance from the granite boundary. A series of laboratory tests on 350 core specimens made by 35 fresh rock blocks obtained from 5 selected locations around Mt. Palgong are performed to verify the variation of physical and mechanical properties related to metamorphic grade of the rock. Water content and absorption ratio of the hornfels linearly increase with distance to the granite boundary whereas dry unit weight, p-wave velocity, point load strength, and slake durability index linearly decrease with the distance. These results imply that the metamorphic grade of the hornfels also linearly decrease with the distance to granite boundary. Empirical equations for the variation of properties with the distance to granite boundary and relationship between a property and another one are deduced by regression analyses. And a criteria for classification of hornfels exposed in the study area based on the P-wave velocity and point load strength is proposed.

• Economic and Environmental Geology
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• v.30 no.5
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• pp.477-491
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• 1997

In the Bibong area of the western part of Chungcheongnam-do, ultramafic masses occur as discontinuous isolated lenticular bodies in the Precambrian Kyeonggi gneiss complex. They extend for about 200 m long to NNE directions which are parallel to fault lines in the gneiss complex. The ultramafic masses contact with the adjacent gneiss complex as steeply dipping faults. They are dunites and harzburgites and many of them are partially or completely serpentinized. The ultramafic rocks dominantly show protogranular, equigranular and equigranular-$m{\grave{o}}saic$ textures. They also show porphyroclastic (megacrystic) or recrystallized textures reflecting several stages of metamorphism. They contain varying amounts of olivine $(Fo_{89-92})$, enstatitic to bronzitic orthopyroxene, diopsidic clinopyroxene, tremolitic to pargasitic hornblende, and spinel with serpentine, talc, chlorite, calcite and magnetite. The ultramafic rocks have high magnesium numbers and transitional element contents, low alkali contents and show deplete REE patterns. Comparing with available data, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to those of worldwide mantle xenoliths and orogenic related ultramafic rocks. The field evidences, petrographical, geochemical and mineralogical characteristics shown in the ultramafic rocks of the Bibong area are similar to alpine type ultramafic rocks emplaced into the crust by the faulting as mantle slab types. With the petrographical characteristics, these mineralogical compositions suggest that the ultramafic rocks of the Bibong area have experienced several stages of retrogressive metamorphism in a condition ranging from the upper amphibolite facies to greenschist facies.