• Economic and Environmental Geology
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• v.8 no.1
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• pp.25-56
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• 1975

Most fluorite deposits of South Korea are distributed in three metallogenic zones namly as: Hwacheon, Hwangangni and Geumsan metallogenic zones. Fluorite deposits of each zone show The characteristic features owing to the geological setting, the structural patterns and their forming processes. deposits of the Hwacheon metallogenic zone are wholly fissure filling hydrothermal veins emThe bedded in shear fractures of the granite gneiss or schists of Precambrian age or in the cooling fractures of the granite and acidic hypabyssal rocks which are assumed to be a differentiated sister rock of the granite. Localization of most fluorite veins of the region is structurally controlled by NW and EW fracture systems and genetically related to the granite intrusion which ascertained as motivating rock of the fluorite mineralization. Fluorites are in most cases accompanied by quartz, chalcedony mainly and rarely agate, calcite, barite and sulphide base metals in some localities. The deposits of the Hwangangni metallogenic zone were formed at the last stage of hydrothermal polymineralization of W, Mo, Cu, Pb, Zn. The majority of the fluorite ore bodies were originated from replacement in limestone beds of Great Limestone Series or in calcareous interbeds of metasediments, whereas some cavity-filling ore bodies were embedded in phyllites and schists of the Ockcheon system and along the fissures in the replaced beds which were originated by volume decrease. The localization of fluorite deposits in this region is genetically related to the Moongyong granite which has been dated as middle Cretaceous, and controlled structurally by the $N20^{\circ}{\sim}50^{\circ}W$ extension fracture system or axial planes of folds, and by faults of NE direction that acted as paths of ore solution. The deposits of the Geumsan metallogenic zone are seemed to be formed through the similar process as that of Hwangangni metallogenic zone, but characteristic distinctions are in that they are more prevailing fracture filling veins and large number of the deposits are localized in roof-pendants or xenolithes of limestone in granites and porphyries. Igneous rocks that presumably motivated the mineraltzation are middle Cretaceous Geumsan granite and porphyries. Metallogenic epoch of the fluorite mineralization of South Korea are puesumably limited in early-middle Cretaceous. Studies of the fluid inclusions in fluorites of the region reveal that the homogenization temperature of the fluorite deposits are as follows: Hwacheon metallogenic zone : $95^{\circ}C{\sim}165^{\circ}C$; Hwangangni metallogenic zone : $97^{\circ}C{\sim}235^{\circ}C$; Geumsan metallogenic zone : $93^{\circ}C{\sim}236^{\circ}C$. Judging from the above results, the deposits of the Hwancheon region were formed at the epithermal stage, and those in the Hwangangni and Geumsan regions, were deposited at epithermal stage preceded by mesothermal mineralization of small scale in which some sulphide minerals were deposited. The analytical data of minor elements in the fluorites reveal that ore solutions of Hwangangni metallogenic zone seemed to be emanated in more acidic stage of magma differentiation than Hwacheon metallogenic zone did.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.273-283
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• 2003

Fissured rock and soft ground always suggest, problems in the construction of the underground space. The stress release of the weak underground material by opening the underground space with a soft ground, fissures and joints can lead to the failure of the opening. Grouting of the weak rock and the soft ground, which is a process of injecting some bonding agents into the soft ground, is one of the measures to reinforce the soft ground and to prohibit the failure of the underground construction due to the stress release. The proper installation of the grouting is essential to ensuring the safety of the tunneling operation, so that the evaluation of the grouting performance is very significant. The general procedure of evaluating the grouting is coring the grouted section and measuring the compression strength of the core. However, sometimes when the grouted section is at the crown of the tunnel and the grouting is installed at a wide section, the coring is not good enough. This study is oriented to propose a new and a non-destructive procedure of evaluating the grouting performance. The proposed method is based on the wave propagation of elastic waves, and evaluates the shear stiffness of the ground and investigates the anomalies such as voids and cracks. The SASW ( Spectral-Analysis-of-Surface-Waves) method is one of the candidate s to make the inspection of the pouting performance, and is adopted in this study. The practical grouting activity was monitored by SASW method, and the proposed method was applied to the inspection of the grouting performance to check the verification of the proposed method.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.400-414
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• 2021

Under high-level radioactive waste repository conditions, bentonite as an engineered barrier material undergoes thermal, hydrological, mechanical, and chemical processes. We report the applications of X-ray Computed Tomography (CT) imaging technique on the characterization and analysis of bentonite over the past decade to provide a reference of the utilization of this technique and the recent research trends. This overview of the X-ray CT technique applications includes the characterization of the bentonite either in pellets or powder form. X-ray imaging has provided a means to extract grain information at the microscale and identify crack networks responsible for the pellets' heterogeneity. Regarding samples of pellets-powder mixtures under hydration, X-ray CT allowed the identification and monitoring of heterogeneous zones throughout the test. Some results showed how zones with pellets only swell faster compared to others composed of pellets and powder. Moreover, the behavior of fissures between grains and bentonite matrix was observed to change under drying and hydrating conditions, tending to close during the former and open during the latter. The development of specializing software has allowed obtaining strain fields from a sequence of images. In more recent works, X-ray CT technique has served to estimate the dry density, water content, and particle displacement at different testing times. Also, when temperature was added to the hydration process of a sample, CT technology offered a way to observe localized and global density changes over time.

• The Korean Journal of Petroleum Geology
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• v.12 no.1
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• pp.1-8
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• 2006

Jiaolai Basin is the Cretaceous continental sedimentary basin developed in Shandong Province of China. It is interpreted as a pull-apart basin which is filled with fluvio-lacustrine sediments and volcanic rocks. The sedimentary strata are divided into three formations: Laiyang Formation, Qingshan Formation and Wangshi Formation in ascending order. Laiyang Formation of the early Cretaceous consists of conglomerate, sandstone and shale, which are grey, black or red in color, respectively. Qingshan Formation of early Cretaceous includes various kinds of volcanic rocks. Late Cretaceous Wangshi Formation consists of red conglomerate, sandstone and shale. Various types of oil shows are observed on many outcrops in the basin such as asphalt filing fissures, oil smelling, rocks wetted with oil. However, commercial oil discovery was not made. Laiyang Formation is the richest in terms of organic matter contents. Some grey or black shales of Laiyang Formation contain more than 1% of organic matter. Kerogens of some layers mainly consist of amorphous organic matter or pollen. Thermal maturity of the organic matter reached main oil generation zone and hydrocarbon genetic potential is fairly good. According to such geochemical data, some layers of Laiyang Formation can act as hydrocarbon source rocks.

• Geophysics and Geophysical Exploration
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• v.4 no.1
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• pp.8-18
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• 2001

To delineate the inhomogeneities including fractures and to estimate the freshness of rock borehole radar consisting of the reflection and tomography methods, and GPR surveys were conducted at a granite quarry mine. The borehole reflection survey using the direction finding antenna was also conducted to get the spatial orientations of reflectors. 20 MHz was adopted as the central frequency for the borehole radar reflection and tomography surveys and 100 MHz was for GPR. Through the interpretation of borehole reflection data using dipole and direction finding antenna as well as GPR images, which are good agreement with each other, we could determine the orientation of the major fractures in three dimensional way. Parts of travel time curves of tomography data showed the anisotropy, which is uncommon in granite quarry. By comparing the tomography data and TeleViewer images, the anisotropy effect in this area are closely related to fine fissures aligned in the same direction. The area confined by the two fractures, MF2 and MF5, might consist of the most fresh granite in the surveyed area, which was concluded from the borehole radar tomography, and GPR images as well as the distribution of anisotropy.

• Economic and Environmental Geology
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• v.26 no.2
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• pp.145-154
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• 1993

Gold-silver deposits in the Kwangyang-Seungju area are emplaced along $N4^{\circ}{\sim}10^{\circ}W$ to $N40^{\circ}{\sim}60^{\circ}W$ trending fissures and fault in Pre-cambrian Jirisan gneiss complex or Cretaceous diorite. Mineral constituents of the ore from above deposits are composed mainly of pyrite, arsenopyrite, pyrrhotite, magnetite, sphalerite, chalcopyrite, galena and minor amount of electrum, tetrahedrite, miargyrite, stannite, covellite and goethite. The gangue minerals are predominantly quartz and calcite. Gold minerals consist mostly of electrum with a 56.19~79.24 wt% Au and closely associated with pyrite, chalcopyrite, miargyrite and galena. K-Ar analysis of the altered sericite from the Beonjeong mine yielded a date of $94.2{\pm}2.4\;Ma$ (Lee, 1992). This indicates a likely genetic tie between ore mineralization and intrusion of the middle Cretaceous diorite ($108{\pm}4\;Ma$). The ${\delta}^{34}S$ values ranged from +1.0 to 8.3‰ with an average of +4.4‰ suggest that the sulfur in the sulfides may be magmatic origin. The temperatures of mineralization by the sulfur isotopic composition with coexisting pyrite-galena and pyrite-chalcopyrite from Beonjeong and Jeungheung mines were $343^{\circ}C$ and $375^{\circ}C$ respectively. This temperature is in reasonable agreement with the homogenization temperature of primary fluid inclusion quartz ($330^{\circ}C$ to $390^{\circ}C$; Park.1989). Four samples of quartz from ore veins have ${\delta}^{18}O$ values of +6.9~+10.6‰ (mean=8.9‰) and three whole rock samples have ${\delta}^{18}O$ values of +7.4~+10.2‰ with an average of 7.4‰. These values are similar with those of the Cretaceous Bulgugsa granite in South Korea (mean=8.3‰; Kim et al. 1991). The calculated ${\delta}^{18}O_{water}$ in the ore-forming fluid using fractionation factors of Bulgugsa et al. (1973) range from -1.3 to -2.3‰. These values suggest that the fluid was dominated by progressive meteoric water inundation through mineralization.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.21-36
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• 2005

Although the main geology of Korea consists of granite and gneiss, it Is not uncommon to encounter anisotropy Phenomena in crosshole radar tomography even when the basement is crystalline rock. To solve the anisotropy Problem, we have developed and continuously upgraded an anisotropic inversion algorithm assuming a heterogeneous elliptic anisotropy to reconstruct three kinds of tomograms: tomograms of maximum and minimum velocities, and of the direction of the symmetry axis. In this paper, we discuss the developed algorithm and introduce some case histories on the application of anisotropic radar tomography in Korea. The first two case histories were conducted for the construction of infrastructure, and their main objective was to locate cavities in limestone. The last two were performed In a granite and gneiss area. The anisotropy in the granite area was caused by fine fissures aligned in the same direction, while that in the gneiss and limestone area by the alignment of the constituent minerals. Through these case histories we showed that the anisotropic characteristic itself gives us additional important information for understanding the internal status of basement rock. In particular, the anisotropy ratio defined by the normalized difference between maximum and minimum velocities as well as the direction of maximum velocity are helpful to interpret the borehole radar tomogram.

• Economic and Environmental Geology
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• v.27 no.2
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• pp.147-160
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• 1994

Copper-bearing hydrothermal vein mineralization of the Samsan area was deposited in two stages (I and II) of quartz-calcite-sulfide veins which fill fissures in Cretaceous volcanic and sedimentary rocks of the Gyeongsang basin. The major ore minerals, chalcopyrite and sphalerite, together with pyrite, galena, hematite, and minor sulfosalts, occur with epidote and chlorite as gangue minerals in stage I quartz veins. Chlorite geothermometry, fluid inclusion and stable isotope data indicate that copper ore was deposited mainly at temperatures between $330^{\circ}C$ and $280^{\circ}C$ from fluids with salinities between 12 and 3 equiv. wt % NaCl. Evidence of fluid boiling indicates a range of pressures from ${\leq}100$ to 200 bars bars. Within ore stage I there was an apparent decrease in ${\delta}^{34}S$ values of $H_{2}S$ with paragenetic time, from 8.0 to 2.3 per mil. This pattern was likely achieved through progressive increases in activity of oxygen accompanying boiling and mixing. In the early part of the first stage, the high temperature, high salinity fluids gave way to progressively cooler and more dilute fluids of the late parts in the first stage and of the second stage. There is a systematic decrease in calculated ${\delta}^{18}O_{water}$ values with decreasing temperature in the Samsan hydrothermal system, from values of -86 per mil for early portion of stage I through -5.9 per mil for late portion of stage I to -6.3 per mil for stage II. The ${\delta}D$ values of fluid inclusion waters also decrease with paragenetic time from -76 per mil to -86 per mil. These trends combined with mineral paragenesis and fluid inclusion data are interpreted to indicate progressive cooler, more oxidizing meteoric water inundation of an early exchanged meteoric hydrothermal system.