정연학 Yeonhak Jung , 김태현 Taehyun Kim , 이용재 Yongjae Lee

DOI: Vol.37(No.4) 155-168, 2024

Studying mineral properties under extreme environments is essential for understanding the processes occurring deep inside the Earth. In order to simulate the high-temperature and high-pressure conditions expected inside the Earth, combined usage of a laser heating system and a diamond anvil cell has been actively developed and established as a standard means in mineral physics research. Reproducing such simultaneous high-temperature and high-pressure environments involves the use of extremely small amounts of sample in a few tens of microns in dimension, which in turn requires high precision and stability of the laser heating system. For this purpose, a double-sided laser heating system has been constructed consisting of a fiber laser, an optical lens system that enables micron-level focusing control, and a spectrometer for temperature measurement. In this paper, we introduce the configuration of a newly constructed double-sided laser heating system and verify its application through a phase transition experiment of feldspar mineral that occurs under the mantle transition zone conditions. The quality of the diffraction data measured for the sample recovered after laser heating under pressure allows the evaluation of the homogeneous phase transition in the heated portion and subsequent analysis using the Rietveld analysis. Such a laboratory-based laser heating system is expected to increase the efficiency of extreme environment experiments at synchrotron facilities.

레이저 가열 시스템, 다이아몬드 앤빌 셀, 상전이, Laser-heating system, Diamond anvil cell, Phase transition

정기영 Gi Young Jeong

DOI: Vol.37(No.4) 169-183, 2024

Samples of kaolin and weathered anorthosite from kaolin deposits in Sancheong, Gyeongsangnamdo, Korea, were subjected to quantitative X-ray diffraction (XRD) analysis after long-term (>30 years) storage. The main constituent minerals were hydrated halloysite and kaolinite, which were formed by weathering of the anorthosite. The hydrated halloysite was partially dehydrated to various intermediate hydration states during long-term storage. The mineral composition of the sample dehydrated at 60℃ was quantified by full pattern fitting of the XRD data using mineral standards separated from Sancheong kaolin. The results showed that the sample contained up to 93% halloysite and up to 65% kaolinite. The relative proportions of halloysite and kaolinite showed a good linear correlation (R²=0.96) between the original samples and the samples dehydrated at 60℃. Although the kaolins in this region are overall dominated by halloysite, they contain relatively variable amounts of halloysite and kaolinite, suggesting that the kaolins followed different weathering pathways. Because halloysite and kaolinite are common secondary minerals in weathering profiles of feldspathic rocks and sediments, quantitative analysis of kaolin minerals will contribute to quantitative studies of mineral cycling in terrestrial environments.

고령토, 풍화, 할로이사이트, 카올리나이트, 정량 XRD, Kaolin, Weathering, Halloysite, Kaolinite, Quantitative XRD

고상모 Sang-mo Koh , Otgon-erdene Davaasuren , 이범한 Bum Han Lee , 신우창 Woochang Shin

DOI: Vol.37(No.4) 185-202, 2024

The study area is located in the Yeongdong-gun, where the Precambrian Sobaeksan Gneiss Complex and Cretaceous sedimentary rocks of the Yeongdong Group are in contact with the Yeongdong Fault. In the northwestern part of the gneiss complex, near the boundary with the Yeongdong Fault, a mica schist formation is distributed. Over the past 20 years, 2-3 companies have been producing sericite in the altered and weathered zones within the mica schist formation. This mica schist is relatively common in sericite and has undergone intense mylonitization due to ductile deformation associated with the shear zone. These mylonites exhibit primary metamorphic foliation, and secondary shear foliation, and have undergone folding and faulting. In this study, we attempted to distinguish the original rocks (protoliths) of the mylonites, specifically gneiss and schist, using a chemical compositional discrimination diagram, particularly the (K₂O+Na₂O) vs. Na₂O diagram. Additionally, we established chemical compositional criteria to differentiate sericite ores from non-ores applicable to the study area. The sericite was formed by the hydration of feldspar and muscovite, with deposits distributed within the shear zone resulting from ductile deformation. It was confirmed that retrograde metamorphism from amphibolite facies to greenschist facies occurred in the brittle-ductile transition zone due to fluid introduction through a fracture zone near the surface. The identified shear zone extends approximately 500 meters in width and over 3 kilometers in length, continuing to the northeast and southwest. Given its scale, it may be more appropriate to refer to it as the Yeongdong Shear Zone rather than the Yeongdong Fault.

견운모, 연성변형작용, 영동단층, 전단대, Sericite, Ductile deformation, Yeongdong Fault, Shear zone

이종환 Jong-hwan Lee , 윤일하 Il-ha Yun , 김순오 Soon-oh Kim

DOI: Vol.37(No.4) 203-213, 2024

A geochemical study was conducted to elucidate the origin of fluorine (F) contained in biotite granite within Oseongsan (OS), Eulwangsan (EW), and Sammokdo (SM) areas, Yeongjong-do, Incheon, Korea. The preceding studies revealed that biotite granites in the study area originated at a similar time (app. 230 Ma, Triassic), but their F contents and petro-mineralogical features are different. Based on the previous results, geochemical analyses of biotite granite were additionally executed to investigate their type and the heterogeneous nature of their source magma. The results suggest that biotite granites of the OS and EW areas were classified as A-type granite, showing much higher contents of F and high field strength elements (HFSEs) and Ga/Al ratio and a stronger negative anomaly of Eu, but they in the SM area were grouped into I-type granite showing the opposite tendency. The F content of the A-type biotite granites showed a stronger positive correlation with the content of heavy rare earth elements (HREEs) and HFSEs, resulting from the formation of complexes with F during the magmatic differentiation. Based on the differences in the contents of F, trace elements, and REEs, the biotite granites in the OS and EW areas were determined as the A-type, but those of the SM area belonged to the I-type. Consequently, the difference in the F content between the regions can be attributed to the different petrochemical properties of biotite granites caused by their origin.

불소, 영종도, 흑운모화강암, A형 화강암, I형 화강암, Fluorine, Yeongjong-do, Biotite granite, A-type granite, I-type granite

최우현 Woohyun Choi , 박창윤 Changyun Park

DOI: Vol.37(No.4) 215-230, 2024

This study examines the alteration mechanisms of zones near the Boam mine in Uljin by analyzing the occurrence and chemical composition of muscovite found with hematite, comparing it to muscovite from the Yuli mica schist and pegmatite-derived muscovite to evaluate its potential as an exploration indicator. Muscovite in the alteration zones appears in two main contexts: in proximal alteration zones at the boundary of pegmatite and limestone, and in distal alteration zones, alternating with phyllite in the Yuli Formation located about 500 m from them. This muscovite, formed as a secondary mineral from late-stage hydrothermal fluids of the pegmatite, commonly precipitates in a replacement or pore-filling pattern. Compared to muscovite in the Yuli mica schist, alteration-zone muscovite shows enrichment in Fe, Mg, and Ti, while it is depleted in Al and Na. In comparison to pegmatite muscovite, it also shows deficiencies in Al, Na, and Li. These chemical features reflect the geochemical characteristics of the final fluids during pegmatite crystallization, likely due to (1) reduced Li mobility due to F depletion in the fluid, (2) Na deficiency in the fluid as a result of extensive albitization in the late crystallization stages, and (3) Fe and Mg enrichment in the late-stage fluid due to interactions with schorl, an Fe-rich tourmaline that crystallized during early silicic melt phases. These findings suggest that the distinct chemical composition of muscovite in alteration zones, compared to that of surrounding host rocks and pegmatites, aids in delineating alteration zones and can serve as a mineralogical indicator in pegmatite exploration.

보암광산, 변질대, 백운모, 열수 유체, 페그마타이트, Boam mine, Alteration zone, Hydrothermal fluids, Muscovite, Li-bearing pegmatite

강인성 Insung Kang , 구태희 Tae-hee Koo , 김진욱 Jinwook Kim

DOI: Vol.37(No.4) 231-236, 2024

1,10-phenanthroline assay and Ferrozine assay are common colorimetric methods for measuring the oxidation state of iron in iron-bearing minerals. However, the application of the 1,10-phenanthroline colorimetric method has not been extensively studied for iron oxide minerals. The present study aims to confirm the effective concentration range of the 1,10-phenanthroline assay and evaluate its applicability to iron oxide minerals by analyzing the degree of iron reduction in maghemite (γ-Fe₂O₃) nanoparticles and partially microbially reduced maghemite nanoparticles. In experiments conducted with FeCl₂ solutions to determine the effective concentration range, the detection limit was confirmed to be within 15-20 mM due to the absorbance measurement limitations of the UV-Vis spectrophotometer, while the upper limit for clearly distinguishing the proportion of ferrous iron was identified as 10 mM. When the 1,10-phenanthroline assay was applied to maghemite nanoparticles and microbially reduced maghemite nanoparticles, consistent ferrous iron proportions were observed up to 8 mM without significant variation across repeated experiments (0.7% and 20%, respectively). By contrast, in the high-concentration group (80 mM), the ferrous iron proportions were found to be significantly overestimated (over 3% and 80%, respectively). The present study confirmed the applicability of the 1,10-phenanthroline assay for the analysis of maghemite nanoparticles used in conjunction with hydrofluoric acid (HF)-sulfuric acid (H₂SO₄) extraction method. Within the effective concentration range (0-20 mM), consistent ferrous iron proportions were observed, confirming that the same analytical procedure used in the field of clay minerals (1,10-phenanthroline assay associated with HF-H₂SO₄ extraction) can also be applied to iron oxide minerals to calculate ferrous iron proportions.

비색법, 1, 10-페난트롤린, 산화철 광물, 자적철석, 철 산화도 계산, Colorimetric method, 10-phenanthroline, Maghemite, Iron oxide, Iron oxidation state calculation

장영준 Yeongjun Jang , 김영규 Yeongkyoo Kim

DOI: Vol.37(No.4) 237-245, 2024

The precipitation of schwertmannite, which exhibits high specific surface area and adsorption properties, is well-known for its ability to remove various oxyanions and heavy metals through co-precipitation and adsorption in acid mine drainage (AMD). However, despite its importance, the co-precipitation of highly toxic antimony (Sb) with schwertmannite and the associated mineral phase transformations and changes in Sb behavior remain poorly understood. This study investigates the co-precipitation and phase transformation reactions between schwertmannite and Sb, which are critical for understanding Sb behavior and removal. Schwertmannite co-precipitated with Sb(OH)₆^- was synthesized, and mineralogical changes were observed under AMD conditions favorable for jarosite precipitation. X-ray diffraction (XRD) and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses confirmed the successful precipitation of Sb-precipitated schwertmannite, with a high co-precipitation efficiency of 97.5%. Sb was stably incorporated into the schwertmannite structure by substituting for Fe instead of sulfate. Phase transformation experiments showed that both pure schwertmannite and Sb-schwertmannite transformed into goethite but did not transition to jarosite. This lack of jarosite transformation is attributed to either insufficient conditions for jarosite formation or differences in the characteristics of Sb compared to arsenate. This study highlights the significance of schwertmannite in influencing Sb behavior in AMD and provides a foundation for improving the efficiency of AMD treatment systems.

슈베르트마나이트, 공침, 자로사이트, 상변화, 안티모니, Schwertmannite, Co-precipitation, jarosite, Phase transformation, Antimony

송석환 Seokhwan Song

DOI: Vol.37(No.4) 247-264, 2024

Dolomites are found nearby Garorim-man, designated as National Marine Ecological Park and majority of the rocks contain NOA (Naturally Occurring Asbestos). With detailed geological investigations, samples were collected at sites assumed as asbestos with dolomite rocks and representative samples were analyzed by PLM (Polarized Light Microscopy), XRD(X-Ray Diffraction), FE-SEM (Field Emission Scanning Electron Microscopy) and EPMA (Electron Probe Micro-Analysis). Amphiboles within the dolomites were asbestiforms or non-asbestiforms. Varying amounts of asbestos minerals, including tremolite and actinolite asbestos, were found within the soils. The asbestos minerals were found near the cracks and fractures as well as along the bedding plane, and occurred as acicular and spherulitic shapes with mass fiber types. Eastern side of the Garorim-man was dominated by tremolite asbestos, but at the western side, by tremolite and actinolite asbestos. Overall results suggest that amphibole type asbestos were originated from the hydrothermal alteration. Considering development situation such as the construction as well as mining claim maps for asbestos minerals, additional detail land management plans for the NOA area needed.

백운암, 자연발생석면, 각섬석계 석면, 토지 관리 방안, Dolomite, Naturally occurring asbestos, Amphibole asbestos, Land management plan

유봉철 Bong Chul Yoo

DOI: Vol.37(No.4) 265-281, 2024

Magnesium (Mg) is a metallic element belonging to the alkaline earth metals, and is essential for the weight reduction of transportation means (automobiles, aircraft, etc.) due to the transformation of industrial structure. Therefore, it is one of the 33 critical minerals selected by the Ministry of Trade, Industry and Energy in 2023. Also, it is one of the critical minerals that requires a lot of effort in exploration in preparation for a unified Korea in the future. The Qingshanhuai magnesite deposit is located in the southwest of the Dashiqiao magnesite belt in northeastern China.The geology of this deposit consists of Paleoproterozoic sedimentary rocks (Liaohe Group) and igneous rocks (dyke, Proterozoic granitoid, Yanshannian granite). The magnesite from this deposit occurs in Member 3 (dolomitic marble and schist) of Dashiqiao formation of the Paleoproterozoic Liaohe group, and it occurs parallel to the hostrock (the dolomite marble). Qingshanhuai magnesite deposit consists of magnesite, dolomite, talc, chlorite, quartz, calcite, apatite, halite, and iron oxide. These minerals, except magnesite, are factor that lower the grade of magnesite. Quartz and halite occur within magnesite, indicating that the magnesite was formed in a silica-rich evaporative environment. Dolomite from this deposit contains 19.65~21.27 wt.% (MgO content), 29.31~31.12 wt.% (CaO content) with minor of FeO, MnO, and As₂O₅ elements, but has almost the theoretical composition of dolomite. Magnesite contains 45.02~47.85 wt.% (MgO content) with monor of FeO, MnO, CaO, and As₂O₅ elements. These minor elements are produced by replacing the MgO element, and it can be seen that the FeO and MnO contents increase together (correlation coefficient: 0.71). Calcite, that filling the fissures in the magnesite, contains a small amount of MgO (4.40 wt.%). Talc contains 29.30~29.97 wt.% (MgO content) and 61.12~62.74 wt.% (SiO₂ content) with minor of Al₂O₃, FeO, CoO, SrO, and As₂O₅ elements. Al₂O₃, CoO, SrO, and As₂O₅ are proportional to the SiO₂ element, and FeO is proportional to the MgO element. The structural formular of chlorite from this deposit is (Mg_4.77-3.59Fe_0.11-0.01Zn_0.01-0.00Co_0.03-0.00Na_0.01-0.00K_0.01-.00Sr_0.02-.00As_0.04-0.00Ca_0.06-0.00Al_1.57-1.01)_5.88-5.32(Si_3.72-2.98Al_1.02-.28)_4.00O₁₀(OH)₈. It indicated that chlorite from this deposit is similar with theoretical chlorite and corresponds to Mg-rich chlorite. Compositional variations in chlorite from this deposit are caused by phengitic or Tschermark substitution (Al^3+,VI+Al^3+,IV <-> (Fe²⁺ 또는 Mg²⁺)^VI+(Si⁴⁺)^IV).

힝샨후아이 마그네사이트 광상, 탄산염암, 녹니석, 산상, 화학조성, Qingshanhuai magnesite deposit, Carbonate, Chlorite, Occurrence, Chemical composition

윤소정 Soh-joung Yoon

DOI: Vol.37(No.4) 283-291, 2024

Illite deposits with illite as the main commodity are rare. Illite, though common in sedimentary rocks, has a relatively short history of its mineral definition and utilization compared to other clay minerals, such as kaolinite or smectite. The shortage of feasibility studies of illite deposits and of the illite mineral value information can make an illite resource/reserve estimation challenging. The author collected information, though limited, such as ore grades, mineral grades, and product prices of illite, which can be used for reasonable ore/mineral value predictions and selection of cut-off grades in (pre-)feasibility studies. Some definitions of illite mineral, mineral resource, and mineral/ore grades are also briefly described in this review.

영동 일라이트, 산업광물, 광물 가치, 세리사이트, Yeongdong illite, Industrial mineral, Mineral value, Sericite

이수진 Soojin Lee , 이현승 Hyunseung Lee , 공정민 Jeongmin Kong , 안다연 Dayeon An , 이용문 Yongmoon Lee

DOI: Vol.37(No.4) 293-300, 2024

This study was conducted as a fundamental study to improve the cation exchange capacity of synthetic zeolite A (LTA) and performance for the selective adsorption of gas molecules such as CO₂, CH₄, and N₂. Structural changes were analyzed using X-ray diffraction at 3.35 GPa and 150℃ to investigate the phase stability and decomposition process under temperature and pressure conditions. The powder diffraction of the sample was measured using a symmetric diamond anvil cell (DAC) and synchrotron X-ray light source under temperature and pressure conditions, and the changes in lattice parameters and bulk modulus were calculated through the LeBail method and the Birch-Murnaghan equation. Zeolite A maintained structural stability up to 2.07 GPa in the presence of H2O, and showed a relatively higher bulk modulus (K0=106(6) GPa) than other zeolite. However, zeolite A undergoes a phase transition to 62.2% of garronite, 18.5% of jadeite, 14.1% of smectite-like materials, and 5.2% of quartz after 2.07 GPa and 150℃. Based on unit cell volume normalized to 10 framework oxygen atoms, the unit cell volume decreased by 42.2% for garronite and 77.3% for jadeite compared to zeolite A.

제올라이트 A, 상안정도, 체적 탄성률, 방사광 X-선원, 다이아몬드 앤빌셀, Zeolite A, Phase stability, Bulk Modulus, Synchrotron X-ray light source, Diamond anvil cell

이현승 Hyunseung Lee , 이수진 Soojin Lee , 공정민 Jeongmin Kong , 안다연 Dayeon An , 이용문 Yongmoon Lee

DOI: Vol.37(No.4) 301-311, 2024

The compressive properties and phase transition processes of natural zeolites, clinoptilolite and stilbite, were investigated using H₂O as a pressure-transmitting medium at up to 3.50 GPa and 250℃. It was observed that both zeolites were hydrated upon contact with H₂O, resulting in slight expansion of unit cell volume. At ca. 2 GPa pressure and heating to 200 ℃, both zeolites underwent decomposition and recrystallization, transitioning to smectite and quartz. The smectite formed from clinoptilolite exhibited a relatively constant d(001) of 11-12 A, while the smectite formed from stilbite showed a larger range of 10-15 A, indicating a greater degree of interlayer hydration. This difference is thought to be influenced by variations in the extraframework cations of the two zeolites, affecting the changes in interlayer cations and the level of hydration in smectite. Additionally, this difference influenced changes in the unit cell volume under pressure. The volume change during the clinoptilolite-smectite transition was approximately 1.1%, while a volume difference of about 19.0% was observed in the stilbite-smectite transition. The results of this study can provide foundational data for understanding the decomposition characteristics of zeolite minerals in high-temperature and highpressure environments, as well as the processes of decomposition, water transport, and mantle density changes in subduction zone contexts.

클리놉틸로라이트, 스틸바이트, 분해, 체적탄성계수, 고온고압, Clinoptilolite, Stilbite, Break down, Bulk modulus, High-temperature and -pressure

김태환 Taehwan Kim

DOI: Vol.37(No.4) 313-325, 2024

Mn-rich quartzose metasedimentary rocks, or manganiferous quartzites originate from chert-dominated deep-sea sediments, and their occurrence is not uncommon in orogenic belts. I analyzed oxygen isotopic compositions of zircon and quartz in a manganiferous quartzite from high-pressure metamorphic belt in northern Victoria Land, Antarctica. This study reports for the first time the oxygen isotopic compositions of zircon and quartz from manganiferous quartzites in the world. Zircon and quartz yielded isotopic variation within 2 ‰ range, and mean δ¹⁸O values of 18.13 ± 0.25 ‰ (2σ) and 20.73 ± 0.26 ‰ (2σ), respectively. These are lower than the median value (~25-28 ‰) of chert, a primary component of the sedimentary protolith, at the time of deposition. Combined with much lower oxygen isotopic composition represented by fluid activity during high-pressure metamorphism, the oxygen isotopic composition of the chert-dominated protolith was reset and lowered by subduction-zone metamorphism in association with terrane accretion event. Calculation of equilibrium isotope fractionation between zircon and quartz implies that the re-equilibration of the oxygen isotopic composition of the manganiferous quartzite protolith by the deep fluid activity took place during the eclogite-facies prograde-to-peak metamorphism rather than retrograde one.

함망간규암, 산소동위원소 조성, 저어콘, 석영, 고압 변성작용, Manganiferous quartzite, Oxygen isotopic composition, Zircon, Quartz, High-pressure metamorphism

정재원 Jaewon Jung , 한동우 Dongwoo Han , 이창열 Changyeol Lee

DOI: Vol.37(No.4) 327-338, 2024

The Ulleung basin located in the East Sea is a back-arc basin formed by the extensional stress owing to the roll-back of the Pacific and Philippine oceanic plates during the Miocene. Previous survey shows that significantly high surface heat flux ranging from 70 to 130mW/m2 across the Ulleung basin, which cannot be explained by the heat anomalies in the upper mantle and excess heat due to the radiogenic isotope decays in the lithosphere. As an alternative, hydrothermal circulation in the fractured and faulted crust, which increases permeability of the crust, could transport the heat energy in the deep crust toward the overlying sediment via heat mining and increase the surface heat flux. Thus, we developed 2-dimensional numerical model which considers both hydrothermal circulation and sedimentation during a formation of the back-arc basin. The numerical model is successfully benchmarked by previous study and the effects of varying permeability and sedimentation rate on the surface heat flux are evaluated. The developed numerical model can be used for the future study which quantitatively unravels the high surface heat flux in the Ulleung basin.

울릉분지, 배호분지, 열수순환, 표면 열류량, 수치모델, Ulleung basin, Back-arc basin, Hydrothermal circulation, Surface heat flux, Numerical model

정원석 Wonseok Cheong , 김윤섭 Yoonsup Kim

DOI: Vol.37(No.4) 339-359, 2024

Tourmaline is a key mineral for reconstructing the geologic history of its host rock. We investigated the occurrence patterns and mineral chemistry of tourmaline in metasedimentary rocks and leucogranites in the northeastern Yeongnam Massif. The study area, characterized by low-pressure, and high-temperature metamorphism, is divided into the sillimanite zone (upper amphibolite facies) and the garnet zone (lower granulite facies) based on the occurrence of garnet in the metapelitic rocks. Therefore, between the two metamorphic zones, the garnet-in isograd can be delineated. In the sillimanite zone, brown euhedral to subhedral tourmaline is present but decomposes into cordierite and sillimanite near the garnet zone. In the garnet zone, tourmaline is either absent or occurs as reddish-brown euhedral to subhedral crystals. Tourmaline breakdown textuers allow delineation of a tourmaline-out isograd (or tourmaline instability isograd). Based on these textures and petrogenetic grids, metamorphic P-T conditions between the tourmaline-out isograd and the garnet-in isograd were estimated at 2-4 kbar and 680-730℃. EPMA analysis show that tourmaline (dravite) composition changes with increasing metamorphic grade: Mg, Ti, and Ca increase, while Fe and X-vacancy decrease. These trends suggest that tourmaline can be used as a geothermometer. In leucogranites, tourmaline is predominantly schorl. Blue tourmaline (dravite) occurs in some metasedimentary rocks and leucogranite, independent of the metamorphic zone, likely formed from late-stage boron-rich fluids during retrograde metamorphism.

전기석, 광물화학, 영남육괴, 저압-고온 변성작용, Tourmaline, Mineral chemistry, Yeongnam massif, LP-HT metamorphism

강지훈 Ji-hoon Kang

DOI: Vol.37(No.4) 361-374, 2024

The Namhu-Gilan area of Andong City is mainly composed of Precambrian metamorphic rocks, Jurassic igneous rocks, Cretaceous sedimentary rocks (Hasandong, Iljik, Hupyeongdong, Jeomgok/Gasongdong Formations), and Cretaceous igneous rocks. Major faults include the WNW-EW-ENE trending Andong fault, which is the boundary fault between Uiseong Block of the Gyeongsang Basin and Sobaeksan Province of the Yeongnam Massif, the Namhu fault parallel to the former, and the (N)NW trending Gilan fault. In this paper, we report the geological structure of the study area analyzed through geometric and kinematic characteristics of beddings, faults, and folds in the vicinity of these faults, and consider the tectonic movements related to the orientation of the Andong and Namhu faults (ANFs). In the south of the ANFs, fold and fault zone [Namhu-Gilan Fold and Fault Zone (NGFFZ)] with about 0.2~2.5 km width and a dip of more than 30°in the direction perpendicular to the Andong fault develops. Within the NGFFZ, bedding poles are arranged on a pi-circle with a low-angleplunging pi-axis parallel to these faults direction, and upright to steeply dipping folds, (conjugate) asymmetric to reversed folds, (conjugate) reverse-slip (low-angle) reverse faults and their accompanying (conjugate) drag folds, and cross-fold joints develop in association with the ANFs movement. The NS trending folds, which refold the ANFs and the NGFFZ, develop in this area. The folds formed by compression in the direction parallel to the ANFs caused various orientations of bedding and the WNW-EW-ENE orientations of the ANFs in the study area. It is considered that the two tectonic movements associated with the formations of the ANFs and the NGFFZ (1st deformation event) and the NS trending folds (2nd deformation event) regionally occurred at least near the boundary between Uiseong Block of the Gyeongsang Basin and Sobaeksan province of the Yeongnam Massif, and in order to verify the presence of inferred Gilan fault further researches are required for the complete geometry of the ANFs.

경상분지, 안동 및 남후 단층, 남북 방향 습곡, 지질구조, Gyeongsang Basin, Andong and Namhu faults, NS trending folds, Geological structure