• Journal of the Mineralogical Society of Korea
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• v.6 no.2
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• pp.80-93
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• 1993

Jido kaolin deposits developed in the rhyolitic tuff of Cretaceous are located in the western part of Sinan-gun, Jeonranam-do. Jido kaolin deposits is predominantly composed of pyrophyllite, kaolinite and illite. On the basis of mineral assemblage Jido kaolin deposits can be divided into three alteraion zone from the center of alteration to the margin; kaolinite, kaolinite-pyrophyillite and pyrophyillite zones. Discriminant analysis show that $Al_2O_3$, $K_2O$, $Na_2O$, CaO of major elements are discriminant elements classifying kaolinite, kaolinite-pyrophyllite and pyrophyllite zones, while in case of trace elements Cr, Ni, Sc, Zn, and Zr are discriminant elements. Kaolin deposits has been formed by the hydrothermal alterations of the volcano rocks such as rhyolitic tuff and lapilli tuff, in late cretaceous. On the basis of the results of X-ray diffraction analysis, the deposits can be classified into three types of minerals assemblages; kaolinite, kaolinite-pyrophyllite and pyrophyllite zones. All the assemblages contain quartz and muscovite, but the kaolinite zone contains kaolinite, illite and chlorite, the kaolinite-pyrophyllite zone contains kaolinite, pyrophyllite and the pyrophyllite zone contains illite and pyrite.

• Economic and Environmental Geology
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• v.24 no.4
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• pp.347-361
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• 1991

The Sangeun ore deposit is located in a volcanic belt within the Gyeongsang Basin in south western Korea. The ore deposit is of representative epithermal Au-Ag quartz vein type developed in lapilli tuff. This paper presents the mineralization with special emphasis on mineral zoning of the deposits. Principal points are summarized as follows: (1) Four stages of mineralization are recognized based on macrostructures. From ealier to later they are stage I(arsenopyrite-pyrite-quartz), stage II(Au-Ag bearing Pb-Zn-quartz), stage III(barren quartz), and stage IV(dickite-quartz). (2) Electrum principally occurs with arsenopyrite and galena in stage II, and has chemical compositions of 72.9-67.1 Ag atom %, and has Ag/Au ratio of 2.69-2.04. (3) Sphalerite varies in its FeS content according to the mineralization stages; 22.03-18.60 mole % FeS and 1.33-0.23 mole % MnS in stage IB, 16.11-8.64 mole % FeS and 1.33-0.23 mole % MnS in stage II. (4) Alteration zones of mineral assemblage, from the vein to the wall-rock, consist of sericite - quartz - pyrite, sericite - quartz - dickite, sericite - chlorite plagioclase respectively.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.201-213
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• 1990

Mineralogy, chemistry, physical property, and fossil abundance have been studied for the samples collected from three weathering profiles, two from the Duho Formation and one from the Hagjeon Formation in the Tertiary sediments in the Pohang area. The mineralogy of the samples from the Duho Formation shows somewhat different from that of the Hagjeon Formation. Kaolinite is more abundant and shows higher crystallinity in samples from the Duho Formation than those in the Hagjeon Formation, but clay mineral assemblage in each weathering profile remain fairly constant with depth. This difference in mineral distribution seems to be inherited from original source materials. It indicates that little or not severe leaching has been taking place in these three weathering profiles. Weathering indicies indicate different degrees of susceptibility to chemical weathering in these two formations. The Duho Formation has a higher degree of susceptibility to weathering than that of the Hagjeon Formation which is mainly due to differences in clay mineral assemblages in both formations. A noticeble colour difference between oxidized and unoxidized zones in each profile can be easily recognized which is definetely due to different decomposition rate organic carbon by various oxidation state from surface to bottom of the profile. Weathering process have also intensively influenced microfossil preservation about up to 7-10 m in depth in the Duho Formation. Consequently, characteristics observed at weathering surface should be used as a subsidiary tool in setting geologic boundary or establishing formation. Great care must be taken to choose sampling site for microfossil study.

• Journal of the Mineralogical Society of Korea
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• v.10 no.1
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• pp.33-44
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• 1997

The reaction path of water-gneiss in 200m borehole at the Soorichi site of Yugu Myeon, Chungnam was simulated by the EQ3NR/EQ6 program. Mineral composition of borehole core and fracture-filling minerals, and chemical composition of groundwater was published by authors. In this study, chemical evolution of groundwater and formation of secondary minerals in water-gneiss system was modelled on the basis of published results. The surface water was used as a starting solution for reaction. Input parameters for modelling such as mineral assemblage and their volume percent, chemical composition of mineral phases, water/rock ratio reactive surface area, dissolution rates of mineral phases were determined by experimental measurement and model fit. EQ6 modelling of the reaction path in water-gneiss system has been carried out by a flow-centered flow through open system which can be considered as a suitable option for fracture flow of groundwater. The modelling results show that reaction time of 133 years is required to reach equilibrium state in water-gneiss system, and evolution of present groundwater will continue to pH 9.45 and higher na ion concentration. The secondary minerals formed from equeous phase are kaolinite, smectite, saponite, muscovite, mesolite, celadonite, microcline and calcite with uincreasing time. Modeling results are comparatively well fitted to pH and chemical composition of borehole groudwater, secondary minerals identified and tritium age of groundwater. The EQ6 modelling results are dependent on reliability of input parameters: water-rock ratio, effective reaction surface area and dissolution rates of mineral phases, which are difficult parameters to be measured.

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.61-87
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• 1995

On the basis of lithology, the Precambrian Hongjesa Granitic Gneiss can be locally zoned into granoblastic granitic gneiss, porphyroblastic granitic gneiss, migmatitic gneiss from its center to the marginal part. There are no distinct differences in mineral assemblages by lithologic zoning, but it partly shows the change of mineral assemblage in the adjacent with migmatitic gneiss, thus mineral assemblage can be subdivided into Zone I and Zone II. In terms of mineral compositions, the characteristics of Zone I are coexisting K-feldspar+muscovite+sillimanite. The characteristics of Zone II are (1) breakdown of muscovite, (2) coexisting garnetScordierite, (3) coexisting garnet+cordierite + orthoamphibole. The Buncheon Granitic Gneiss is mainly composed of augen gneiss. In the adjacent area with Honjesa Granitic Gneisses, Buncheon Granitic Gneiss has the mineral assemblage of sillimanite+biotite+K-feldspar+(kyanite). Kyanite occurs as relict grains in the Buncheon and Hongjesa Granitic Gneissess. Kyanite shows anhedral to subhedral form and coexists with sillimanite in only one of these samples. Garnet from a migmatitic gneiss (Zone 11) has relatively high $X_{Fe}$ value in core and rim. Garnet from a porphyroblastic granitic gneiss(Zone I) has relatively homogemeous core but compositionally-zoned rim. Biotites show various colour from greenish-brown, brown to reddish brown at maximum adsorption. Also, the Ti, and Mg content in biotites increases from Zone I to Zone II. The plagioclases shows the chemical composition of $Ab_{84}An_{16}$ -$Ab_{70}An_{30}$ (oligoclase) in Zone I and $Ab_{70}An_{30}$ -$Ab_{50}An_{50}$(andesine) in Zone 11. These variations indicate that the gneisses in the study area experienced a upperamphibolite facies. The presence of kyanite as relict grains indicates that the metamorphic rocks in this area exprienced a high-temperature/medium-pressure type metamorphism, followed by high-temperaturellow-pressure metamorphism. Metamorphic P-T conditions for each gneiss estimated from various geothermobarometers and phase equilibria are 698-$729^{\circ}C$/6.3-11.3 kbar in augen gneiss, 621-$667^{\circ}C$/1.0-5.4 kbar in migmatitic gneiss, and 602-$624^{\circ}C$/1.9-3.4 kbar in porphyroblastic granitic gneiss. These data suggest that the study area was subjected to a clockwise P-T path with isothermal decompression (dP/dT=about 60 bar/$^{\circ}C$).

• Economic and Environmental Geology
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• v.38 no.3 s.172
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• pp.347-353
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• 2005

The geology of the Tumbang Lapan area consists of Permian to Carboniferous metamorphic rocks, Cretaceous granitic rocks, and Permian to Tertiary sedimentary and volcanic rocks. Three faults are developed in surveyed area, and are functioned as channels of the hydrothermal solution which farmed quartz veins within tuff3. In the mineralized area, argillic and propylitic alterations are dominant. Argillic altered rocks show the alteration mineral assemblages of kaolinte+sericite+quartz+chlorite+pyrite. Mineral association in propylitic alteration is chlorite+epidote+feldspar+quartz+pyrite+ magnetite. Vein type, fracture filling, stockwork are observed in survey area. As a result of analysis of samples from quartz veins and altered rocks, some mineralized rocks showed $0.01\~4.6g/t$ of gold.

• Economic and Environmental Geology
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• v.25 no.1
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• pp.41-50
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• 1992

Mineral assemblages, mineral chemistries and stable isotope compositions of altered rocks of the Ogmae, Seongsan, Haenam and Gusi mines near the Haenam volcanic field in the southwestern part of the Korea peninsula were studied. Characteristic hydrothermal alteration zones in these deposits occurring in the Cretaceous volcanics and volcanogenic sediments, acidic tuff, and rhyolite, were outlined. Genetic environment with particular reference to the spatial and temporal relationships for these deposits were considered. The alteration zones defined by a mineral assemblage in the Ogmae and Seongsan deposits can be classified as alunite, pyrophyllite, kaolinite or dickite, quartz, illite or illite/smectite. Alunite was not developed in the Gusi and Haenam deposits. Boundaries between the adjacent zones are always gradational except for vein-type alunite. Alteration zones are superimposed upon each other in some localities. These deposits formed $71.8{\pm}2.8{\sim}76.6{\pm}2.9$ Ma ago, which is the almost same age of later volcanic rocks $79.4{\pm}1.7{\sim}82.8{\pm}1.2$ Ma, the Haenam Group, corresponding to Campanian. It indicates that hydrothermal alteration of these deposits appeared to be related to felsic volcanism in the area. Consideration of the stability between kaolinite, alunite, pyrite and pyrophyllite, and the geothermometry based on the mineral chemistry of illite and chlorite suggests that the maximum formation temperature for alunite and pyrophyllite can be estimated at about $250^{\circ}C$ and $240{\sim}290^{\circ}C$, respectively. It also suggests that these deposits were formed by acidic sulfate solution with high aqueous silica and potassium activity in a shallow depth environment. Compositional variation of alunite also suggests that the physico-chemical conditions fluctulated considerably during alteration processes, indicating shallow depth environment. The Haenam deposit was formed at a relatively greater depth than the others. The sulfur isotope composition of alunite and pyrite indicates that sulfur probably had a magmatic source, and the oxygen isotope composition for kaolinite indicates that the magmatic hydrothermal solution was diluted by circulating meteoric water.

• Economic and Environmental Geology
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• v.28 no.2
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• pp.93-108
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• 1995

The Bobae sericite deposit occurs in rhyodacite of the Cretaceous volcanogenic sedimentary rocks, Upper Yucheon Group, in the western part of Pusan. The alteration zones are divided into the phyllie and prophylitic zone based on the mineral assemblages. The phyllic zone is subdivided into three subzones; Andalusite-Pyrophyllite, Sericite and Albite subzones. Oxides vs. $Al_2O_3$ contents show variations corresponding to mineral assemblage in each alteration zone. On the basis of bulk chemical compositions, it was found that $SiO_2$ increases in the Andalusite-Pyrophyllite subzone and $K_2O$ in the Sericite subzone. The oxygen, hydrogen and sulfur isotope analysis indicates that the fluids were originally derived from the residual magmatic solution. It has been mixed with abundant meteoric water later. The ore-forming temperatures obtained from sericite (illite) geothermometer are about $250{\sim}350^{\circ}C$. Considering the phase stability relation, PoT conditions of the andalusite-pyrophyllite subzone were estimated to be less than 0.5 kb and almost $400^{\circ}C$, respectively. The K-Ar ages of sericites indicate that the clay deposit is genetically related to the Cretaceous-Paleogene Masan Hornblende-Biotite Granite.

• Economic and Environmental Geology
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• v.47 no.6
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• pp.601-610
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• 2014

Udo is the site of a short-lived monogenetic submarine volcanic vent which builts basaltic clastic deposits below sea level, by early Surtseyan-type explosive eruption and later effusive lava eruptions. Mineral assemblage, major and trace element chemistry indicate that the Someori sub-alkaline lava flows were related to the WPTB(within plate tholeiitic basalt) rather than IAT(island-arc tholeiite) and that the geotectonic regime of Korean Peninsula went away from the subduction zone after the Later Miocene.

• Economic and Environmental Geology
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• v.19 no.spc
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• pp.43-52
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• 1986

Kaolin-pyrophyllite are locally abundant in the three hydrothermal areas at Yangsan-Tongnae area, Hadong-Sancheong area and Haenam area, deposits are originally composed of acidic volcanic rocks and anorthositic rocks in Hadong-Sancheong area. The clay deposits are formed in the near shallow depths environment through acid hydrothermal alteration. Hadong-Sancheong halloysite deposits are formed by alteration of anorthosite. These differences are mainly on the various country rocks, geological structure and properties of hydrothermal solutions. Country rock is mostly underlain by rhyolitic tuffaceous and anorthositic rocks and a large number of clay deposits were formed during volcanic activity through upper Cretaceous-lower Tertiary. Intrusive rocks is broadly distributed in this area and clay deposits are variable in shapelayer and funnel typed. Zonal pattern of mineral assemblage is as follows, Yangsan-Tongnae deposits-kaolinite, pyrophyllite, dumortierite, andalusite and sericite, Hadong-Sancheong-mostly halloysite, and Haenam-dickite, pyrophyllite, alunite and diaspore. The difference in the zonal pattern of altered rock is considered to depend on differences in the initial acidity of related hydrothermal solution, initial acidity was controlled by the oxygen fugacity.