• The Journal of the Petrological Society of Korea
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• v.25 no.1
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• pp.29-37
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• 2016

A "granite boulder", ~70 cm in size, was reported from the Geumgang Limestone, and has been considered as a glaciogenic dropstone. Since this interpretation has enormous implications for unraveling the evolution history of the Ogcheon Metamorphic Belt, we re-examined the contact relationship and structure of the "granite boulder", and estimated its emplacement age based upon SHRIMP U-Pb zircon dating. The weighted mean $^{206}Pb/^{238}U$ age pooled from 6 spot analyses of two specimens is $170{\pm}2Ma$ ($2{\sigma}$, MSWD=2.2). This zircon age suggests that the "granite boulder" in the Geumgang Limestone is a part of Jurassic granite, rather than a glaciogenic dropstone.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.1
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• pp.53-64
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• 2020

The Samgwang deposit has been one of the largest deposits in Korea. The deposit consists of series of host rocks including Precambrian metasedimentary rocks and Jurassic Baegunsa formation, which unconformably overlies the Precambrian metasedimentary rocks. The deposit consists of eight lens-shaped quartz veins which filled fractures along fault zones in Precambrian metasedimentary rock, which feature suggest that it is an orogenic-type deposit. Laminated quartz veins are common in the deposit which contain minerals including quartz, ankerite, white mica, chlorite, apatite, rutile, arsenopyrite, sphalerite, chalcopyrite and galena. The structural formulars of white micas from laminated quartz vein and wallrock alteration are determined to be (K_1.02-0.82Na_0.02-0.00Ca_0.00)(Al_1.73-1.58Mg_0.26-0.16Fe_0.23-0.10Mn_0.00Ti_0.03-0.01Cr_0.01-0.00)(Si_3.35-3.22Al_0.79-0.65)O₁₀(OH)₂ and (K_0.75-0.67Na_0.01Ca_0.00) (Al_1.78-1.74Mg_0.16-0.15Fe_0.15-0.13Mn_0.00Ti_0.04-0.02Cr_0.01-0.00)(Si_3.33-3.26Al_0.74-0.67)O₁₀(OH)₂, respectively. It suggest that white mica from laminated quartz vein has higher interlayer cation (K+Na+Ca) and Fe+Mg+Mn+Ti content in octahedral site compared to the white mica from the wallrock alteration. Compositional variations in white mica from laminated quartz vein can be caused by phengitic or Tschermark substitution ((Al³⁺)^VI+(Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI)+(Si⁴⁺)^IV) and (Fe³⁺)^VI <-> (Al³⁺)^VI substitution. Ankerite from laminated quartz vein has compositional variations of FeO and MgO contents along crystal growth direction. The geochemical and textural features suggest that laminated quartz vein from the Samgwang gold-silver deposit was formed during ductile shear stage, which is an important main gold-silver ore-forming event in orogeinc deposit.

• Economic and Environmental Geology
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• v.47 no.6
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• pp.571-588
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• 2014

It consists of the Precambrian Jirisan metamorphic complex and Sancheong anorthosite complex and the Mesozoic granitoids which intrude them in the Sancheong area, the Jirisan province of Yeongnam massif, Korea. The study area is located in the western part of the stock-type Sancheong anorthosite complex. We performed a detailed fieldwork on the Sancheong anorthosite (SA) and Fe-Ti ore body (FTO) which constitute the Sancheong anorthosite complex, and reinterpreted the origin of FTO foliation and the genetic relationship between them from the foliations, shear zones, occurrences of the SA and FTO. The new structural characteristics between them are as follows: the multilayer structures of FTO, the derived veins of straight, anastomosing uneven types and block structures related to the size reduction of SA, the gradual or irregular boundaries of SA blocks and FTO showing bulbous lobate margins and comb structures, the FTO foliation and linear arrangements of flow occurrence which is not ductile shear deformation, the discontinuous shear zone of SA, the orientation of FTO foliations parallel to the boundaries of SA blocks, the predominance of FTO foliations toward the boundaries of SA blocks and being proportional to the aspect ratio of plagioclase xenocrysts and SA xenoblocks, and the flow folding structures of FTO foliation. Such field evidences indicate that the SA is not fully congealed when the FTO is melt and the fracturing of partly congealed SA causes the derived veins of FTO and the size reduction of SA. Also the gradual or irregular boundaries of SA blocks and FTO result from the mutual reaction between the not fully congealed SA blocks and the FTO melt, and the FTO foliation is a magmatic foliation which was formed by the interaction between the FTO melt and the partly congealed SA blocks. Therefore, these suggest that the SA and FTO are not formed from the intrusion of different magmas in genesis and age but from a coeval and cogenetic magma through multiple fractionation. We predict that the FTO will show an very irregular occurrence injected along irregular fractures, not the regular occurrence like as the intrusive vein and dike. It can be applied to the designing of Fe-Ti mineral resource exploration in this area.

• Economic and Environmental Geology
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• v.52 no.1
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• pp.107-118
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• 2019

Two assertions about the process the formation of the high-purity limestone in the Taebaeksan Basin, categorized into syngenetic and epigenetic origin, are verified on the basis of its oxygen-carbon stable isotopic characteristics. The carbonate rocks sampled from the selective six high-purity limestone mines and several outcrops in the Daegi formation are featured by various colors such as the gray, light gray and dark gray. They show a wide range of oxygen stable isotope ratios (4.5 ~ 21.6 ‰), but a narrow range of carbon stable isotope ratios (-1.1 ~ 0.8 ‰, except for vein calcite), which means that they had not experienced strong hydrothermal alteration. In addition, there is no difference in the range of the oxygen stable isotope ratios by mine and color, and it is similar to the range from surrounding outcrop samples. These results indicate that the effect of the hydrothermal alteration were negligible in the generation of high-purity limestone in deposit scale. Whereas, the carbonate rocks can be divided texturally into two groups on the basis of an oxygen isotope ratio; the massive-textured or well-layered samples (>15 ‰), and the layer-disturbed (or layer-destructed) and showing over two colors in one sample (<15 ‰). In the multi-colored samples, the bright parts are characterized by the very low oxygen stable isotope ratios, compared to the dark parts, implying the increase in brightness of the carbonate rocks could be induced by the interaction between hydrothermal fluid and rock. However, these can be applied in a small scale such as one sample and are not suitable for interpretation of the generation of high-purity limestone as a deposit scale. In particular, the high oxygen isotope ratios from the recrystallized white limestone suggest that hydrothermal fluids are also rarely involved during recrystallization process. In addition, the occurrences of the high-purity limestone orebody strongly support the high-purity limestone in the area are syngenetic rather than epigenetic; the high-purity limestone layers in the area show continuous and almost horizontal shapes, and is intercalated between dolomite layers. Consequently, the overall reinterpretation based on the sequential stratigraphy over the Taebaeksan basin would play an important role to find additional reserves of the high-purity limestone.

• Korean Journal of Heritage: History & Science
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• v.46 no.1
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• pp.268-289
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• 2013

The Dinosaur tracksite at Jeori, Geumseongmyeon, Euiseonggun, Gyeongsangbukdo, Korea (National Monument No. 373) has been studied in the aspects of location, stratigraphy, sedimentology, fossil occurrence, unique geological records, literature, significance in natural history, preservation, and management. On the basis of these features, the Jeori tracksite has been assessed semiquantitavely. The Jeori tracksite occurs in the Sagok Formation (Albian) of the Euiseong sub-basin, and over 300 footprints forming 12 sauropod trackways, 10 ornithopod trackways, and 1 theropod trackways are preserved in this tracksite. The track-bearing deposits consist of tabular-bedded medium- to fine-grained arkose with mudstone drape, interlaminated fine-grained sandstone to siltstone and mudstone, and shaly mudstone. The dinosaur tracks are preserved in the interlaminated fine-grained sandstone to siltstone and mudstone, and most of them are observed as underprints. The track-bearing deposits are interpreted as sheetflood deposits on the floodplain under a seasonal paleoclimatic condition with alternating of wetting and drying periods. Multiple tension fractures with NE strike were formed in the track-bearing bed, which resulted in that tracks seem to occur in several horizons. The significance in natural history of the tracksite can be summarized as follows: 1) the historical implication of the Jeori tracksite as the firstly designated National Monument of dinosaur fossil sites, 2) the high density of the occurrence of diverse footprints (over 300) within small area (about $1,600m^2$), and 3) the significance of the tension fractures associated with the track-bearing bed as geoeducational records for the understanding the development of fault. In order to share the value of the Jeori tracksite in the aspect of natural history with the community and public, the interpretive panel should be modified to include figures explaining paleoenvironment and tension fault development. In addition it is recommended that a brochure be published briefly explaining the tracksite and to educate the residents about the natural and social significance of the tracksite. For the safety of visitors it would be desirable for the road in front of the tracksite to be moved at least 10 m southward, which could mitigate the shaking of the track bed caused by traffic.

• Korean Journal of Mineralogy and Petrology
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• v.34 no.1
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• pp.1-14
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• 2021

The Unsang gold deposit has been one of the three largest deposits (Daeyudong, Kwangyang) in Korea. The geology of this deposit consists of series of host rocks including Precambrian metasedimentary rock and Jurassic Porphyritic granite. The deposit consists of Au-bearing quartz veins which filled fractures along fault zones in Precambrian metasedimentary rock and Jurassic Porphyritic granite, which suggests that it is an orogenic-type deposit. Quartz veins are classified as 1) galena-quartz vein type, 2) pyrrhotite-quartz vein type, 3) pyrite-quartz vein type, 4) pegmatic quartz vein type, 5) muscovite-quartz vein type and 6) simple quartz vein type based on mineral assembles. The studied quartz vein is pyrite-quartz vein type which occurs as sericitization, chloritization and silicification. The white mica from stylolitic seams of laminated quartz vein occurs as fine or medium aggregate associated with white quartz, pyrite, chlorite, rutile, monazite, apatite, K-feldspar, zircon and calcite. The structural formular of white mica from laminated quartz vein is (K0.98-0.86Na0.02-0.00Ca0.01-0.00Ba0.01-0.00 Sr0.00)1.00-0.88(Al1.70-1.57Mg0.22-0.09Fe0.23-0.10Mn0.00Ti0.04-0.02Cr0.01-0.00V0.00Ni0.00)2.06-1.95 (Si3.38-3.17Al0.83-0.62)4.00O10(OH2.00-1.91F0.09-0.00)2.00. It indicated that white mica of laminated quartz vein has less K, Na and Ca, and more Si than theoretical dioctahedral micas. Compositional variations in white mica from laminated quartz vein are caused by phengitic or Tschermark substitution [(Al3+)VI+(Al3+)IV <-> (Fe2+ or Mg2+)VI+(Si4+)IV] and direct (Fe3+)VI <-> (Al3+)VI substitution. The structural formular of chlorite from laminated quartz vein is((Mg1.11-0.80Fe3.69-3.14Mn0.01-0.00Zn0.01-0.00K0.07-0.01Na0.01-0.00Ca0.04-0.01Al1.66-1.09)5.75-5.69 (Si3.49-2.96Al1.04-0.51)4.00O10 (OH)8. It indicated that chlorite of laminated quartz vein has more Si than theoretical chlorite. Compositional variations in chlorite from laminated quartz vein are caused by phengitic or Tschermark substitution (Al3+,VI+Al3+,IV <-> (Fe2+ or Mg2+)VI+(Si4+)IV) and octahedral Fe2+ <-> Mg2+ (Mn2+) substitution. Therefore, laminated quartz vein and alteration minerals of the Unsan Au deposit was formed during ductile shear stage of orogeny.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.3
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• pp.167-183
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• 2023

The Janggun Pb-Zn deposit consists of Mn orebody, Pb-Zn orebody and Fe orebody. The Mn orebody composed of manganese carbonate orebody and manganese oxide orebody on the basis of their mineralogy and genesis. The geology of this deposit consists of Precambrian Weonnam formation, Yulri group, Paleozoic Jangsan formation, Dueumri formation, Janggum limestone formation, Dongsugok formation, Jaesan formation and Mesozoic Dongwhachi formation and Chungyang granite. This manganese carbonate orebody is hydrothermal replacement orebody formed by reaction of lead and zinc-bearing hydrothermal fluid and Paleozoic Janggum limestone formation. The wallrock alteration that is remarkably recognized with Pb-Zn mineralization at this hydrothermal replacement orebody consists of mainly rhodochrositization with minor of dolomitization, pyritization, sericitization and chloritization. Carbonates formed during wallrock alteration on the basis of paragenetic sequence are as followed : Ca-dolomite (Co type, wallrock) → ankerite and Ferroan ankerite (C1 type, early stage) → ankerite (C2 type) → sideroplesite (C3 type) → sideroplesite and pistomesite (C4 type, late stage). This means that Fe and Mn elements were enriched during evolution of hydrothermal fluid. Therefore, The substitution of elements during wallrock alteration beween dolomitic marble (Mg, Ca) and lead and zinc-bearing hydrothermal fluid (Fe, Mn) with paragenetic sequence is as followed : 1)Fe ↔ Mn and Mn ↔ Mg, Ca, Fe elements substitution (ankerite and Ferroan ankerite, C1 type, early stage), 2)Fe ↔ Mn, Mn ↔ Mg, Ca and Mg ↔ Ca elements substitution (ankerite, C2 type), 3)Fe ↔ Mn, Fe ↔ Ca and Mn ↔ Mg, Ca elements substitution (sideroplesite, C3 type), and 4)Fe ↔ Mg, Fe ↔ Mn and Mn ↔ Mg, Ca elements substitution (sideroplesite and pistomesite, C4 type, late stage)

• Korean Journal of Mineralogy and Petrology
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• v.35 no.4
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• pp.469-484
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• 2022

The Janggun Pb-Zn deposit has been known one of the four largest deposits (Yeonhwa, Shinyemi, Uljin) in South Korea. The geology of this deposit consists of Precambrian Weonnam formation, Yulri group, Paleozoic Jangsan formation, Dueumri formation, Janggum limestone formation, Dongsugok formation, Jaesan formation and Mesozoic Dongwhachi formation and Chungyang granite. This Pb-Zn deposit is hydrothermal replacement deposit in Paleozoic Janggum limestone formation. The wallrock alteration that is remarkably recognized with Pb-Zn mineralization at this deposit consists of mainly rhodochrositization and dolomitization with minor of pyritization, sericitization and chloritization. Wallrock alteration is divided into the five zones (Pb-Zn orebody -> rhodochrosite zone -> dolomite zone -> dolomitic limestone zone -> limestone or dolomitic marble) from orebody to wallrock. The white mica from wallrock alteration occurs as fine or medium aggregate associated with Ca-dolomite, Ferroan ankerite, sideroplesite, rutile, apatite, arsenopyrite, pyrite, sphalerite, galena, quartz, chlorite and calcite. The structural formular of white mica from wallrock alteration is (K_0.77-0.62Na_0.03-0.00Ca_0.03-0.00Ba_0.00Sr_0.01)_0.82-0.64(Al_1.72-1.48Mg_0.48-0.20Fe_0.04-0.01Mn_0.03-0.00Ti_0.01-0.00Cr_{0.00As0.01-0.00}Co_0.03-0.00Zn_0.03-0.00Pb_0.05-0.00Ni_0.01-0.00)_2.07-1.92 (Si_3.43-3.33Al_0.67-0.57)_4.00O₁₀(OH_1.94-1.80F_0.20-0.06)_2.00. It indicated that white mica from wallrock alteration has less K, Na and Ca, and more Si than theoretical dioctahedral micas. The white micas from wallrock alteration of Janggun Pb-Zn deposit, Yeonhwa 1 Pb-Zn deposit and Baekjeon Au-Ag deposit, and limestone of Gumoonso area correspond to muscovite and phengite and white mica from wallrock alteration of Dunjeon Au-Ag deposit corresponds to muscovite. Compositional variations in white mica from wallrock alteration of these deposits and limeston of Gumoonso area are caused by mainly phengitic or Tschermark substitution mechanism (Janggun Pb-Zn deposit), mainly phengitic or Tschermark substitution and partly illitic substitution mechanism (Yeonhwa 1 Pb-Zn deposit, Dunjeon Au-Ag deposit and Baekjeon Au-Ag deposit), and mainly phengitic or Tschermark substitution and partly illitic substitution or Na⁺ <-> K⁺ substitution mechanism (Gumoonso area).

• Korean Journal of Mineralogy and Petrology
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• v.36 no.4
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• pp.273-288
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• 2023

The Gubong Au-Ag deposit, which has been one of the largest deposits (Unsan, Daeyudong, Kwangyang) in Korea, consists of eight lens-shaped quartz veins (a mix of orogenic-type and intrusion-related types) that filled fractures along fault zones within Precambrian metasedimentary rock. Korea Mining Promotion Corporation found a quartz vein (referred to as the No. 6 vein with a grade of 27.9 g/t Au and a width of 0.9 m) at a depth of -728 ML by drilling (No. 90-12) conducted in 1989. Korea Mining Promotion Corporation conducted drilling (No. 04-1) in 2004 to investigate the redevelopment's possibility of the No. 6 vein. The author studied the occurrence and chemical composition of chlorite and white mica using wallrock, wallrock alteration and quartz vein samples collected from the No. 04-1 drilling core in 2004. The alteration of studied samples occurs chloritization, sericitization, silicification and pyritization. Chlorite and white mica from mineralized zone at a depth of -275 ML occur with quartz, K-feldspar, calcite, rutile and pyrite in wallrock alteration zone and quartz vein. Chlorite and white mica from ore vein (No. 6 vein) at a depth of -779 ML occur with quartz, calcite, apatite, zircon, rutile, ilmenite, pyrrhotite and pyrite in wallrock alteration zone and quartz vein. Chlorite from a depth of -779 ML has a higher content of Al and Mg elements and a lower content of Si and Fe elements than chlorite from a depth of -275 ML. Also, Chlorites from a depth of -275 ML and -779 ML have higher content of Si element than theoretical chlorite. Compositional variation in chlorite from a depth of -275 ML was mainly caused by phengitic or Tschermark substitution [Al^{3+,VI + Al3+,IV} <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV], but compositional variation from a depth of -779 ML was mainly caused by octahedral Fe²⁺ <-> Mg²⁺ (Mn²⁺) substitution. The interlayer cation site occupancy (K+Na+Ca+Ba+Sr = 0.76~0.82 apfu, 0.72~0.91 apfu) of white mica from a depth of -275 ML and -779 ML have lower contents than theoretical dioctahedral micas, but octahedral site occupancy (Fe+Mg+Mn+Ti+Cr+V+Ni = 2.09~2.13 apfu, 2.06~2.14 apfu) have higher contents than theoretical dioctahedral micas. Compositional variation in white mica from a depth of -275 ML was caused by phengitic or Tschermark substitution [(Al³⁺)^VI + (Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV], illitic substitution and direct (Fe³⁺)^VI <-> (Al³⁺)^VI substitution. But, compositional variation in white mica from a depth of -779 ML was caused by phengitic or Tschermark substitution [(Al³⁺)^VI + (Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV] and direct (Fe³⁺)^VI <-> (Al³⁺)^VI substitution.

• The Journal of the Petrological Society of Korea
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• v.24 no.4
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• pp.323-335
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• 2015

Although the Daljeon Basalt in the Pohang Basin is important for interpreting the basin evolution, its relative chronology, stratigraphic position, and isotopic age still remain controversial. In order to clear up the controversies, this study carried out detailed field investigation to determine its distribution and occurrence together with reanalysis of its previous geochemical data and $^{40}Ar/^{39}Ar$ age dating. Based upon the field investigation, the basalt occurring in the central part of the Pohang basin is composed of three main bodies and a dozen of minor dikes and sills that intruded into the Yeonil Group. Their mineral assemblages consist of phenocrysts such as olivine and clinopyroxene and fine groundmasses of clinopyroxene, plagioclase, olivine, and opaque oxide, impling the porphyritic texture of alkaline basalt. All their geochemical data also show the similar geochemical characteristics in TAS, Zr-Ti, and REE/trace elements distribution diagrams. The samples are plotted on alkalic field in the total alkali-versus-silica diagram and show similar patterns to enrichment oceanic basalt or within plate basalt in trace elements. In addition, $^{40}Ar/^{39}Ar$ isochron age of 13.82Ma is obtained. These results indicate that the Daljeon Basalt is an alkaline intrusive rock belonging to the middle Miocene Yeonil Group.