• The Journal of the Petrological Society of Korea
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• v.28 no.2
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• pp.129-141
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• 2019

The Eoraesan area, Chungju, which is located in the northwestern part of Ogcheon Metamorphic Zone, Korea, mainly consists of the Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks which intruded it. The metaacidic rocks (MAR) of the Gyemyeongsan Formation show a maximum radioactive value, and the Early Jurassic biotite granite is regionally distributed in this area. In this paper is researched the microstructure related to the growth of rare-earth mineral of allanite in the MAR, and is considered the source and occurrence time of rare-earth element (REE) mineralization. The MAR is mainly composed of alkalic feldspar (mainly microcline), quartz, iron-oxidizing mineral, biotite, muscovite, plagioclase, hornblende, allanite, zircon, epidote, fluorite, apatite, garnet, (clino)zoisite etc. The radioactive elements contained in the allanite cause a dark brown hale in the surrounding biotite, and the allinte also occurs as aggregate along the regional foliation. The deflection of regional foliation and the strain shadows, which are common to the pre-tectonic porphyroblast grown before the formation of regional foliation, can't be observed around most allanites (aggregates). The grain size and orientation of ironoxidizing mineral included in the allanite aggregate are the same as those in the matrix. It is recognized the hydrothermal conversion of hornblende to biotite due to the intrusion of igneous rock, and the secondary biotite occurs and contacts with allanite, zircon, epidote etc. These microstructures indicate that the rare-earth mineral of allanite (aggregate) grew by the hydrothermal alteration due to the intrusion of igneous rock after the formation of regional foliation. It is considered that the REE mineralization is closely related to the intrusion of Early Jurassic biotite granite which is regionally distributed in this area.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.61-68
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• 2023

This study analyzed and compared the physicochemical characteristics of topsoil and subsoil of Grade 1 soil from an igneous rock area on the ecological and nature map. The water content and pH of the collected soil samples were measured, and X-ray fluorescence and X-ray diffraction analyses were performed. The results showed that the water content of the topsoil was higher than that of the subsoil, and its pH was more acidic than that of the subsoil. According to the X-ray fluorescence analysis results, sample I9 was closest to kaolinite, while sample I7 was most distant from kaolinite. All other samples were located between samples I7 and I9. The X-ray diffraction analysis showed that the average content of clay minerals was higher in the topsoil than in the subsoil. The most notable clay minerals produced included illite, vermiculite, kaolinite, chlorite, and gibbsite. The results of this study will be used as a basic data for topsoil restoration to convert subsoil into topsoil.

• Journal of Korean Society of Forest Science
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• v.54 no.1
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• pp.25-35
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• 1981

Some physical and chemical properties of forest soils in Korea were analyzed for providing the reasonable management methods of forest lands, Among 375 soil series surveyed until 1979, 93 soil series of forest soils were classified and analyzed according to their characteristics. Firstly soil data were classified into 5 categories by weathered products and secondly were classified and analyzed by parent rocks. The results are as follows: 1) In forest soils characterized by weathered products volcanic ash soils were proved to be the most fertile and alluvial soils were turned out to be the most infertile soils. Residual soils on mountain and hill were mostly on the average in all kinds of soil properties analyzed except total soil depth. 2) Igneous rocks developed rather infertile soils containing large amount of organic matter and available $P_2O_5$ with relatively deep soil depth and strong acidity. On the other hand sedimentary rocks produced rather shallow soils containing small amount of organic matter and available $P_2O_5$ but they were relatively fertile with weak acidity. 3) Among igneous rocks basalt and trachyte produced very fertile soils and granite and andesite produced slightly infertile soils. 4) Among sedimentary rocks limestone soils had high fertility neutral in acidity but low amount of available $P_2O_5$ 6) Alluvial sand produced generally very infertile soils with great soil depth comparing with the arable alluvial land with high fertility.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.41-54
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• 2012

The weathering process of rocks leads to the reduction of geotechnical bearing capacity. The weathering of granite is frequently used to refer to the degradation of geotechnical property in the design and construction of infra-structure. In this study, the range of values of CIA (chemical index of alteration) and the change of mineral compositions by weathering have been analysed with igneous rock, which covers 45.5% in South Korean territory. Several weathering indices were studied for various rocks found in Korea and significant relationships between different indices were delineated via statistical analysis. The applicability of CIA was found to be the most significant among all weathering indicies. The composition of illite, the secondary weathering residual, generally increases for the felsic rock, and swelling clay material is not included. The weathering of felsic rock will follow a sequential process, starting from bed rock, illite, and chlorite to kaoline. The mafic rock will show weathering process, from bed rock, smectite, and chlorite to kaoline. The intermediate rocks such as andesite and tuff will show similar weathering procedure and the composition of kaoline, chlorite, and smectite tends to increase more than that of illite when the mafic rock is dominated. This means the increase of rock material which has high CEC (cation exchange capacity) during secondary weathering process. However, the characteristics of a specific rock cannot be completely analyzed using merely CIA, since it is exclusively based on chemical composition and corresponding alteration. The CIA can be used to quantify the weathering process in a limited range, and further considerations such as rock composition, strength characteristics will be required to configure the comprehensive weathering impact on any specific region.

• Economic and Environmental Geology
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• v.50 no.5
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• pp.375-387
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• 2017

Amphibolite-hosted Fe-Ti mineralization at the Soyeonpyeong Island, located in central western part of the Korean Peninsula is a typical orthomagmatic Fe-Ti oxide deposit in South Korea. The amphibolite intruded into NW-SE trending Precambrian metasedimentary rocks. Lower amphibolite is characterized by igneous layering, consisting of feldspar-dominant and amphibole-Fe-Ti oxide-dominant layers. The igneous layering shows complicated and/or sharp contact. In contrast, upper amphibolite has a more complicated lithofacies (garnet-bearing, coarser, and schistose), and massive Fe-Ti oxide ore alternates with schistose amphibolite. NS- and EW-trending fault systems lead to redistribute upper amphibolite-hosted Fe-Ti orebody and igneous layering of lower amphibolite, respectively. The whole-rock compositions of amphibolite and Fe-Ti oxide ore reflect their constituent minerals. Amphibolite shows significantly positive Eu anomalies whereas Fe-Ti oxide ore has weak negative Eu anomalies. Plagioclase (Andesine to oligoclase) and Fe-Ti oxide minerals have constant composition regardless of their distribution. Amphibole has a compositionally variable but it doesn't reflect the chemical evolution. Mineral compositions within individual layers and successive layers are relatively constant not showing any stratigraphic evolution. This suggests that there are no successive injections of Fe-rich magma or assimilation with Fe-rich country rocks. Contrasting Eu anomalies between amphibolite and Fe-Ti oxide ore also suggest that extensive plagioclase fractionation during early crystallization stage cause increase in $Fe_2O_3/FeO$ ratio and overall Fe contents in the residual magma. Thus, Fe-rich residual liquids may migrate at the upper amphibolite by filter pressing mechanism and then produce sheeted massive Fe-Ti mineralization during late fractional crystallization.

• The Journal of the Petrological Society of Korea
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• v.17 no.4
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• pp.222-230
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• 2008

Intruding ages for the Jurassic(${\sim}Triassic$) granites in South Korea can be reestablished as $210{\sim}170\;Ma$ and $180{\sim}160\;Ma$ according to the tectonic provinces of magma emplacement. Most Jurassic granites in the Gyeonggi massif have the intrusion ages of $180{\sim}160\;Ma$, indicative of middle Jurassic igneous activity. On the other hand the intrusion ages ($210{\sim}170\;Ma$) for the Jurassic granites in the Yeongnam massif represent late Triassic to middle Jurassic igneous activity. Using the concept of granite suite/supersuite, the Jurassic granites in South Korea can be hierarchically divided into two supersuites and two suites. Huge batholith of NE-SW direction in the Gyeonggi massif could be designated to be 'Gyeonggi Supersuite', which was originated from the mixture of igneous protolith and more evoloved crustal materials and formed in the post-orogenic environment after collision of the north China and south China blocks. There are one supersuite and two suites in the Yeongnam massif 'Yeongnam Supersuite' could be designated from the NE-SW trend batholith in the massif. This supersuite was originated from the mixture of igneous protolith and evolved crustal materials. Granitic rocks between Andong and Girncheon areas could be defined as 'Andong Suite'. This suite was originated from the mixture of depleted mantle and igneous protolith. The Daegang and Hamchang granties could be designated as 'Daegang Suite'. This suite was formed in the anorogenic environment which was different from the orogenic environment of the other supersuite/suite in the Yeongnam massif.

• 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.

• The Journal of Engineering Geology
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• v.27 no.1
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• pp.67-79
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• 2017

Evaluation of the weathering index using the quantitative element composition of rocks is very effective in predicting the degree of weathering of rocks and the secondary weathering residuals. While the process of weathering varies according to the types of rocks, the study of weathering in Korea is concentrated on acidic igneous rocks. This study calculated the weathering indices using whole rock analysis (X-ray fluorescence analysis) of sandstone, mudstone, and shale belonging to clastic sedimentary rocks. The statistical significance of the indices was examined based on the correlation of the calculated weathering indices. Clastic sedimentary rocks showed higher significance of Wp, CIA, CIW and PIA weathering index indicating weathering of feldspar. Chemical Index of alteration (CIA) has the advantage of predicting weathering pathway and clay mineral production, but it is effective to consider chemical index of weathering index (CIW) simultaneously to improve accuracy. In order to reduce uncertainties due to carbonate rocks and to estimate the accurate weathering index, rock samples with high CaO content should be excluded from the evaluation of weathering index.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.108-120
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• 1996

This study reports petrography and geochemical characteristics of the Cretaceous volcanic rocks that are distributed in the vicinity of the Cheonsungsan area, Yangsan-Gun, Gyeongsangnam-Do. The Cretaceous volcanic rocks composed of andesitic rocks, Wonhyosan tuff, Cheonsungsan tuff in ascending order. Sedimentary rock is the basement in the study area cofered with volcanic rocks. These volcanic rocks are Wonhyosan tuff and Cheonsungsan tuff that represented the early phase of the Bulgugsa igneous activity. Wonhyosan tuff are classified into dacite tuff and dacite welded tuff based on the rock texture and their mineral composition. They are covered with Cheonsungsan tuff. Dacite tuff composed of lithic lapilli ash-flow tuff and vitric ash-flow tuff. Most dacite welded tuff are lapilli ash-flow tuff. Cheonsungsan tuff overlying the Wonhyosan tuff consists of rhyolite tuff and rhyolite welded tuff. Rhyolite tuff are lithic crystal ash-flow tuff and crystal vitric ash-flow tuff with somewhat accidental fragments of andesitic and sedimentary rocks. Rhyolite welded tuff is distinguishe from rhyolite tuff by is typical eelded fabrics and its rock color. According to petrochemical data, the volcanic rocks in study area belong to high-K orogenic suties. On the discriminant diagrams such as La/Yb versus Th/Yb, these rocks falls into the discriminant fields for the normal continental margin arc.

• Economic and Environmental Geology
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• v.17 no.4
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• pp.299-314
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• 1984

The Yeongdo Island in Busan City is a remnant of the latest Cretaceous volcano, and consists geologically of andesites, rhyolite tuff, pelitic and psammitic hornfelses, lapilli rhyodacite tuff of the Yucheon Group, felsite and felsite porphyry of the Bulgugsa intrusives, and Holocene sediments in ascending order. The hornfelses are bound to the Taejongdae Formation. The stratigraphic position of the Formation is determined definitely into the Yucheon Group, thus the geologic age is approximately the same with the volcanic rocks of the Group. The sediments had been thermally metamorphosed to make pelitic and psammitic hornfelses of the albite epidote hornfels facies by the effects of active hydrothermal circulation, vaporization, and hybridization of andesitic solution, or of basification of acidic intrusives. Thus, on occasion, those hornfelses are not used to be distinguished from the andesitic rocks in the southeastern part of the Korean peninsula. The paleocurrent direction determined from several cross-beddings of the Taejongdae Formation is suggested to be from southwest to northeast. Orbicular rocks occur in hornfelsed rhyolite tuff, pelitic- and psammitic-hornfelses, and felsite porphyry at a lot of outcrops in the area of southwestern shoreline of the Yeongdo Island. Orbicules in rhyolite tuff and hornfels in the island might have originated from diffusion processes of metasomatic metamorphism carried out by hydrothermal solution rised from the intrusive adamellite which may be emplaced deeply under the Yeongdo volcanics. Those orbicules are due to metasomatic, secondary, and epigenetic origin. Proto-, multi-shelled, and multi-cored orbicules are described in the orbicular tuff. But multi-cored orbicules are not found in the orbicular fornfels. 250 tuff-orbicules numbered sporadically are in $20,000m^2$ area of the locality of orbicular tuff. About 60 hornfels-orbicules occurred sporadically are in $1,700m^2$ area of the locality of orbicular hornfels in the Taejongdae Formation. Orbicules in felsite porphyry might have originated by diffusion reaction between xenoliths and a quiescent zone in felsite porphyry magma. Those are of igneous, primary, and syngenetic origin.