• Journal of the Korean earth science society
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• v.34 no.4
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• pp.329-335
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• 2013

Based on mineral assemblages, field occurrences, the volcanic rocks distributed in the Geumdang Island area are divided into three types: rhyolite, porphyritic rhyolite and intermediated dyke rock. In a diagram of [TAS (total alkali-silica)], rhyolites and porphyritic rhyolites belong to the rhyolite-dacite field and rhyolite field, respectively. As to the times when the rhyolite and porphyritic rhyolite rocks were formed a whole rock K-Ar age was obtained. These absolute age determinations have revealed that the former (rhyolite) has an age of 76-78 Ma and belongs to the Late Cretaceous (Campanian) and the latter (porphyritic rhyolite) is 71-72 Ma in age and thus belongs to the boundary between the Campanian and Maastrichtian. These geological ages are associated with the igneous activity of the Yuchon Group which occurred vigorously in the southern part of the Korean peninsula during the Late Cretaceous. The various geological ages of volcanic rocks distributed in the southwestern part of the peninsula and of igneous rocks found in the Cretaceous formation which contain a wide variety of minerals indicate that in this area, volcanic activities continued vigorously as a result of the collision of the Eurasian and Pacific Plates between 108-71 Ma.

• Journal of the Mineralogical Society of Korea
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• v.19 no.3 s.49
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• pp.197-207
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• 2006

In the coal-bearing formations of the Janggi Group, which are reported as typical clastic sediments, several beds of volcaniclastic rocks are actually found in the Yeongil area. The coal-bearing formations generally exhibit alternating lithologic characteristics of pyroclastic and epiclastic sedimentary facies. Tuff and tuffaceous sandstone rich in pumice fragments are characteristic in the coal-bearing fermations. Diagenetic minerals found in the pyroclastic rocks of the upper and lower coal-bearing formations are montmorillonite, clinoptilolite, opal-CT, and quartz. Several tuffaceous beds correspond to the low-grade ores of zeolites and bentonite, and moreover, these ores mostly occur as thin beds less than 1 m in thickness. Thus, the potential of altered tuffaceous rocks as the resources typical of zeolite and bentonite seems to be low. However, based on mineral composition and CEC determinations, it can be evaluated that these tuffaceous rocks mostly have the promising potential for utilization as the absorbent-functional mineral resources such as acid clays, if these low-grade ores plus adjacent tuffaceous rocks are collectively exploited.

• Economic and Environmental Geology
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• v.2 no.3
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• pp.47-57
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• 1969

The Yeonhwa Lead and Zinc Mine is located in northern part of Kyeongsang-Buk-Do, Korea, and is economically most important mine because it produces most part of the output of lead and zinc minerals in the country. Ore deposits of the mine are localized in the Pungchon Formation and several limestone seams of upper Myobong Formation in Cambrian Age. Ore solution ascended along the fractures of N-S, NE-SW or NW-SE trends and along slate and limestone boundary, and then replaced selectively limestone to make ore bodies. Skarn minerals are consisted of hedenbergite, diopside, and main sulfide mineral orebodies are composed of galena, zincblende, pyrrhotite, pyrite and a minor amounts of arsenopyrite and chalcopyrite. Metal ratio, ${\rho}_{Pb}={\frac{Pb(%)}{Pb(%)+Zn(%)}}{\times}100$, illustrates the zona I arrangements of some ore bodies. It will be inferred the flow trending of ore solution and the process reaction with adjacent country rocks. The sub-divided formations of the Pungchon limestone and Myobong slate are very useful as a criteria for detecting probable ore location. Rhodochrosite veins are good evidence for searching of ore location, especially on Pb-rich ore bodies.

• The Journal of Engineering Geology
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• v.10 no.1
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• pp.51-62
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• 2000

The $CO_2$-richrich water pumps or springs out at two sites (Sinchon and Kohran) consisting of Cretaceous sedimentary rocks in Kyungpook area. The water has been long known as its soda pop-liketaste and therapeutic effect against calcium deficit, stomach and skin troubles, etc. The water arecharacterized by a high $CO_2$ concentration $(P_{CO2}=0.29~l.01 atm)$ and electrical conductance (1,093~2,810$\mu$S/cm). The $CO_2$-rich water belongs to Ca(Na)-$HCO_3$ type in chemical classification. The contents of Ca, Mg, Na, HCO$_3$ and Fe of $CO_2$-rich water show much higher values than those of general groundwater Environmental isotopic data $(^2H/^1H, ^{18}O/^{16}O and ^3H/^1H)$ indicate that the water is ofmeteoric origin recharged after 1950s. The $CO_2$ in the springs seems to be originated from deep-seatedsource related to acidic porphyry and granite nearby sedimentary rocks. Carbonate minerals and albiteare likely to be the major source minerals of the dissoved inorganic constituents in the $CO_2$-rich water.The equilibrium state between major minerals and $CO_2$-rich water was calculated by a thermodynamicprogram.

• 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 ...).

• Journal of the Mineralogical Society of Korea
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• v.7 no.1
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• pp.49-61
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• 1994

As the groundwater flows along the fractures of crystalline rocks, it will be in contact with the fracture walls mostly coated by secondary minerals which are quite different form those of host rocks. The presence of fracture-filling minerals in crystalline rocks is important on the view point of radioactive waste disposal because of their great surface reactivity. The Surichi drill hole of 200 m in depth in the Yugu area composed mainly of Precambrian gneiss was selected to study the formation process of clay minerals on the fracture wall of gneiss, and their relation with present groundwater. The water-rock interaction in fractures resulted in the formation of gibbsite and clay minerals. They are formed by two different processes : (1) Incongruent dissolution of feldspar by groundwater diffused from a fracture path into rock matrix produced smectite and illite in situ, (2) on the wall of fracture, gibbsite, kaolinite, smectite and illite are formed by precipitation of dissolved species in groundwater. They show the paragenetic sequence such as gibbsite${\leftrightarrow}$kaolinite${\leftrightarrow}$smectite or illite. The paragenetic sequence of fracture-filling minerals was controlled by increase of pH of groundwater, decrease of fracture permeability by precipitation of fillings, and immobility of alkali or alkaline earths in groundwater. The groundwater from the Surichi borehole is a $Na-HCO_{3}$ type with pH range of 8.6-9.2. The sodium and bicarbonate in groundwater would be supplied by the dissolution of albite and calcite, respectively. The saturation index of groundwater and surface water calculated by WATEQ4F indicates that gibbsite and kaolinite are under precipitation to equilibrium state, and that smectite and illite are under equilibrium to redissolution environment. The stability relation of clay minerals in the $Na_{2}O-Al_{2}O_{3}-SiO_{2}-H_{2}O$ system shows that kaolinite is stable for all waters.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.285-289
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• 2005

The Cenozoic Era consists of two period , the Tertiary and the Quaternary Period. Weak rock types may include areas containing: 1) poorly cemented or uncemented sediments, 2) highly weathered rock, or 3) fault lines. Especially this paper deal with poorly cemented or uncemented sedimentary rocks in slope. Mechanical weathering is caused by physical processes such as absorption and release of water, and changes in temperature and stress at or near the exposed rock surface. It results in the opening of discontinuities, the formation of new discontinuities by rock fracture, the opening of grain boundaries, and the fracture or cleavage of individual mineral grains. Decomposition causes some silicate minerals such as feldspars to change to clay minerals. There was a strong negative correlation between water absorption and important engineering properties such as strength and durability.

• Journal of the Mineralogical Society of Korea
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• v.1 no.1
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• pp.48-62
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• 1988

The high aluminous meta-claystones are thinly bedded to metasedimentary rocks which belong to Chununsan Formation. Major high aluminous minerals in the ores ae andalusite, kaolinite and pyrophyllite. The other significant constituents are sericite, chloritoid and carbonaceous material, etc. Ores can be classified into 4 types according to mineral compositions; andalusite- kolinite-sericite, andalusite-kaolinite-chloritoid, kaolinite-sericite-pyrophyllite, and kaolinite-chloritoid-sericite ore. The formation of ore minerals are resulted from sedimentary, diagenetic, metamorphic and hydrothermal processes. Andalusite are formed by low-grade metamorphism under the conditions of $400~500^{\circ}C$ and below 4kb, from the view-point of mineral stability field, illite-mica crystallinity and graphitization degree of the carbonaceous material. Andalusites are partly altered to kaolinite, forming major mineral phase in the ores.

• Economic and Environmental Geology
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• v.25 no.3
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• pp.259-273
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• 1992

The Seongsan mine is one of the largest dickite deposits in the southwestern part of the Korean Peninsula. The main constithent minerals of the ore are dickite and quartz with accessory alunite, kaolinite and sericite. The geology around the Seongsan mine consists mainly of the late Cretaceous felsic volcanic rocks. In the studied area, these rocks make a synclinal structure with an axis of E-W direction plunging to the east. Most of the felsic volcanic rocks have undergone extensive hydrothermal alteration. The hydrothermally altered rocks can be classified into the following zones: Dickite, Dickite-Quartz, Quartz, Sericite, Albite and Chlorite zones, from the center to the margin of the alteration mass. Such zonal arrangement of altered rocks suggests that the country rocks, most of which are upper part of the rhyolite and welded tuff, were altered by strongly acid hydrothermal solutions. It is reasonable to consider that initial gas and solution containing $H_2S$ and other compounds were oxidized near the surface, and formed hydrothermal sulfuric acid solutions. The mineralogical and chemical changes of the altered rocks were investigated using various methods, and chemical composition of fifty-six samples of the altered rocks were obtained by wet chemical analysis and X.R.F. methods. On the basis of these analyses, it was found that some components such as $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO, MgO, $K_2O$, $Na_2O$ and $TiO_2$ were mobilized considerably from the original rocks. The formation temperature of the deposits was estimated as higher than $200^{\circ}C$ from fluid inclusion study of samples taken from the Quartz zone. On the basis of the chemical composition data on rocks and minerals and estimated temperatures, the hydrothermal solutions responsible for the formation of the Seongsan dickite deposits were estimated to have the composition: $m_{K^+}=0.003$, $m_{Na^+}=0.097$, $m_{SiO_2(aq.)}=0.008$ and pH=5.0, here "m" represents the molality (mole/kg $H_2O$).

• Economic and Environmental Geology
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• v.29 no.2
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• pp.119-127
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• 1996

Electrum-sulfide minerals of the Namsan Au-Ag mine were deposited in two stages of quartz and calcite veins that fill fault planes in Mesozoic granitic rocks (230~155 Ma). The K/Ar radiometric dating of hydrothermal sericite indicates that mineralization is early Cretaceous age ($127{\pm}3.0Ma$). Mineralogic, fluid inclusion and sulfur isotopic data show that ore minerals were deposited at temperatures between $340^{\circ}C$ and $200^{\circ}C$ from fluid with salinities of 3 to 6 equiv. wt % NaCl. Evidence of fluid boiling (and $CO_2$ effervescence) indicates a maximum pressures of 100 bars. The formation temperature and $fs_2$, of Au-mineralization from the Namsan mines are mainly $280{\sim}230^{\circ}C$ and $10^{-11}{\sim}10^{-13}$ atm, respectively. Au deposition was likely a result of boiling caused to chemical change (pH, $f_{O2}$, ${\Sigma}_{H_2S{\cdot}{\cdot}}$) of ore-fluids. Sulfur isotope composition of sulfide minerals (${\delta}^{34}S=5.1$ to 8.2‰) are consistent with ${\delta}^{34}S_{{\Sigma}{H2S}}$ value of +6 to +7‰, suggesting an igneous source of sulfur partially mixed with wall-rock sulfur.