• The Journal of Engineering Geology
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• v.14 no.3 s.40
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• pp.273-285
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• 2004

The mechanical properties of the Cretaceous tuff distributed in the Goheung area were measured in the laboratory. Tuff (Goehung tuff and Palyeongsan welded tuff) in the study area is classified into vitric tuff with regard to its composition. The specific gravity, the dry density, the water content, the porosity and absorption ratio in tuffs of the study area are 2.51, $2.52(g/cm^2)$, 0.12($\%$), 4.51($\%$) and 1.91($\%$) in means, respectively. In the tuffs, dry densities are in inverse Proportion to Porosities, and absorption ratios are highly proportional with Porosities. The uniaxial compressive strengths(UCS) in the tuffs ranges from 80.4 to 208(MPa) and the average of the strength is 141.1(MPa). According to the engineering classification of intact rock (Deere & Miller, 1966), the tuffs are assigned to the high strength rocks. The point load strength index ($Is_a$) in axial test is 4.2(MPa) on the average, and the point load strength index ($Is_d$) in diametral test is 2.2(MPa) in mean, and the point load strength anisotrophic index($Ia_{(50)}$) by the ratio of $Is_a$ to $Is_d$ is 1.93. There is close linear correlation between the uniaxial compressive strength and point load strength index, and the equation representing the correlation is postulated as follows : UCS = 22 $Is_{(50)}$ +49 (MPa) (r=0.95). It is considered that this equation is a useful tool to estimate UCS for tuff in Goheung area.

• Economic and Environmental Geology
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• v.11 no.2
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• pp.59-68
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• 1978

Of more than 30 varieties of zeolite group minerals, 7 varieties, mordenite, clinoptilolite, natrolite laumontite, stilbite, stellerite and chabazite are identified in Korea, whereas mordenite and clinoptilolite occur in Miocene sediments of small Yonil tertiary basin, east coast of Korea. The basin consists of three separate groups of sediments called Janggi, Gampo and Haseo, which are not correlated stratigraphyically yet. Zeolite occurs alternating with montmorillonite layers in Nuldaeri, Yongdongri and Haseori tuffs of Jahanggi, Gampo and Haseo Groups respectively. Zeolite was formed by diagenesis. of acidic volcanic tuffs.

• Advances in concrete construction
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• v.3 no.1
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• pp.71-90
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• 2015

In order to investigate the feasibility and advantage of tuff used as pozzolan in cement-based composite, the representative specimens of tuff were collected, and their chemical compositions, proportion of vitreous phase, mineral species, and rock structure were measured by chemical composition analysis, petrographic analysis, and XRD. Pozzolanic activity strength index of tuff was tested by the ratio of the compression strength of the tuff/cement mortar to that of a control cement mortar. Pozzolanic reaction degree, and the contents of CH and bond water in the tuff/cement paste were determined by selective hydrochloric acid dissolution, and DSC-TG, respectively. The tuffs were demonstrated to be qualified supplementary binding material in cement-based composite according to relevant standards. The tuffs possessed abundant $SiO_2+Al_2O_3$ on chemical composition and plentiful content of amorphous phase on rock texture. The pozzolanic reaction degrees of the tuffs in the tuff/cement pastes were gradually increased with prolongation of curing time. The consistency of CH consumption and pozzolanic reaction degree was revealed. Variation of the pozzolanic reaction degree was enhanced with the bond water content and relationship between them appeared to satisfy an approximating linear law. The fitting linear regression equation can be applied to mutual conversion between pozzolanic reaction degree and bond water content.

• Economic and Environmental Geology
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• v.18 no.2
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• pp.125-134
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• 1985

The Chisulryoung Volcanic Formation comprises a thick sequence of pyroclastic flow deposits. Six members are distinguished, each representing separate flow units, comprising weakly to intensely welded acidic tuffs. A stock of welded acidic tuff, 1 km in diameter, intrudes hornblende granodiorite and sediments of Late Cretaceous age and the lower part of the Chisulryoung Volcanic Tuff Formation and may represent the vent through which the upper flows of the Chisulryoug Volcanic Formation were erupted.

• 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 the Petrological Society of Korea
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• v.18 no.2
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• pp.137-151
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• 2009

Synthetic analyses of field data, including rock facies, contact relationships, petrography, structural elements, and etc., and previous geochemical and absolute age data of the Tertiary Churyeong Breccia and its surrounding volcanics in the Gyeongju city, Korea, have led to the following results. (1) The Tertiary rocks are divided into the dacitic tuffs, Churyeong Breccia, and andesitic rocks in ascending order. The dacitic tuffs are unconformably overlain by the Churyeong Breccia which is intruded by or conformably overlain by the andesitic rocks. (2) The dacitic tuffs are correlated with the Paleocene${\sim}$Eocene Wangsan dacitic volcanics, while the Churyeong Breccia and andesitic rocks are correlated with the early Early Miocene Andongri Formation and Yongdongri Tuffs in the Waeup Basin, respectively. (3) The Churyeong Breccia accumulated rapidly in the NE-trending graben about 1.5 km in width during the crustal extension in the NW-SE direction due to the East Sea opening. (4) Dacitic${\sim}$andesitic volcanism and crustal extension were active during the early Early Miocene times in SE Korean peninsula. During the deposition the Churyeong Breccia, especially, the volcanism ceased for some time, but the active normal faulting led to the formation of grabens in places.

• Economic and Environmental Geology
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• v.21 no.1
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• pp.1-15
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• 1988

This is a study on the mineral compositions, SK numbers of refractoriness and the genesis of the clay mineral deposits in Cheonnam Province and Handong area. 1. Jindo kaolin deposits: Chief clay minerals of the deposits are kaolinite, quartz and alunite. The SK number of the ore is from $34^+$(the highest) to 27(the lowest). On the genesis of the deposits some geologists believe that the deposits were formed by the alteration of the siliceous tuff. But the deposits seems to be formed by the hydrothermal alteration of the rhyolite lava beds. This area is formed by alternative beds of tuff; and kaoline deposits. 2. Hadong area: Chief mineralogy of Hadong kaolin area is $10{\AA}$ halloysite and kaolinite. The SK number of some of the ore is up to $36^+$. The theoretic SK number of kaolinitic composition is 35. So one of the highest alumina minerals of gibbsite is formed in the ores of $36^+$ SK numbers. 3. Hampyong kaolin deposits: Most of kaolin has black color. The chief minerals are kaolinite, quartz and muscovite. Some of the kaoline contains rutile crystals. SK number ranges from 30 to 17. The kaolin deposit is formed by the transported sedimentation in lower part of the seashore. 4. Jangsan kaoline deposits: Chief minerals of the kaolin is kaolinite, quartz and muscovite. Some kaoline contains small crystals of pyrite. This area consists almost of the tuffs. Kaolin deposits also would be formed by the alteration of the tuffs. 5. Nohwado pyrophyllite deposits: Quartz and pyrophyllite are chief minerals. SK number of the ore ranges from 32 to 30. The pyrophyllite deposits would be formed by the hydrothermal alteration of the rhyolitic lava beds. This area consists of alterative beds of tuffs and rhyolitic lavas. 6. Songsuk pyrophyllite deposits: Chief minerals are quartz, kaolinite, pyrophyllite and iron oxides. In the pyrophyllite deposits egg-like inclusions of diaspore and kaolinite in composition. This area almost consists of tuffs. Several faults are developed and along the fault the tuff would begin to alter to pyrophyllite and some parts to diaspore and kaolinite nodules by the acts of hydrothermal solution.

• Journal of the Geological Society of Korea
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• v.54 no.5
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• pp.513-527
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• 2018

We have carried out granulometry and component analysis on pyroclastic deposits of the Maljandeung Tuff, Ulleung Island, to interpret the eruption types and prime dynamic mechanisms. It is divided into three members in the extracaldera area, each of which comprises the lithofacies of coarse tuffs and lapillistones in the lower part, and pumice deposits in upper one. The lithofacies present quantitative evidences in the granularity and component distribution patterns. As compared to the pumice deposits, the coarse tuffs and lapillistones exhibit a relative increase in both the lithic/juvenile and the crystal/juvenile ratios, and a preferential fragmentation of the juvenile fraction. The abundance of lithics and crystals in the tuffs and lapillistones can be attributed to preferential fragmentation of the aquifer-hosting rocks due to explosive evaporation of ground water, and indirect enrichment in lithics and crystals due to removal of juvenile fines from eruptive cloud. The above data exhibit that early phreatopmagmatic phase was followed by purely magmatic fragmentation phases. The coarse tuffs and lapillistones suggest phreatoplinian eruption derived from explosive interaction of magma with ground water near the conduit, while pumice deposits indicate magmatic eruption by magmatic explosion from juvenile gas pressure. In early stage, phreatoplinian eruption occurred from explosive magma/water interaction in connecting confining water with drawdown of the magma column in the conduit; Later it shifted to plinian eruption by explosive expansion of only magmatic volatiles in intercepting water influx due to higher magmatic gas pressure than confining water pressure with rising of the magma column in the conduit.

• Economic and Environmental Geology
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• v.40 no.3 s.184
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• pp.319-330
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• 2007

The Muposan Tuff is a stratigraphic unit which is distinguished as a cooling unit in the volcanic rocks of the northeastern Kyeongsang Basin. The Muposan Tuff commonly belongs to tuff field according to the granulometric classification and to vitric tuffs according to the constituent classification. The tuffs are mostly densely to partially welded to include very flattened and sometimes stretched pumices and shards, and involve several flow indicator and lateral gradings in maximum diameter and content of their constituents. Movement pattern from flow lineation, lithic and pumice imbrications, asymmetric flow folds, and lateral gradings in maximum diameter and content of their constituents indicate that the Muposan Tuff had a source from the southeastern part.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.59-71
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• 1990

Magnetic anisotropy of a total of 213 independently oriented Tertiary rock samples from Pohang-Ulsan area has been studied. The sampled strata comprise basalts, tuffs and black shale, and range in age from Eocene to Miocene. The previous palaeomagnetic studies indicate that their magnetic carrier minerals are titanomagnetites. Among 23 sampled sites, 11 sites were found to preserve magnetic load foliation parallel to the bedding plane caused by the Iithostatic load of the overlying strata. Other 4 sites showed magnetic lineation indicating the flow direction of lava and tuffs. The remaining 8 sites revealed the magnetic tectonic foliation nearly vertical to the bedding plane. This magnetic foliation is interpreted to be generated by tectonic compression which acted nearly horizontally during the solidification stage of the strata. The compression directions deduced from the tectonic foliation of the 8 sites can be grouped into internally very consistent two group: a N-S trending one and the other WNW-ESE trending one. It is interpreted that the former N-S compression was associated with the N-S spreading of the East Sea(Sea of Japan) and the dextral strike-slip movement of the Yangsan-Ulsan fault system. The latter WNW-ESE compression is interpreted to represent the folding and reverse faulting activity in the Korean and Tsushima straits during middle/late Miocene times.