• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.57-72
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• 2000

The Murzuk Basin covers an area in excess of $350,000{\cal}km^2$, and is one of several intra-cratonic sag basins located on the Saharan Platform of North Africa. Compared with some of these basins, the Murzuk Basin has a relatively simple structure and stratigraphy, probably as a result of it's location on a the East Saharan Craton. The basin contains a sedimentary fill which reaches a thickness of about $4,000{\cal}m$ in the basin centre. This fill can be divided into a predominantly marine Paleozoic section, and a continental Mesozoic section. The principal hydrocarbon play consists of a glacial-marine sandstone reservoir of Cambro-Ordovician age, sourced and sealed by overlying Silurian shales. The present day borders of the basin are defined by tectonic uplifts, each of multi-phase generation, and the present day basin geometry bears little relation to the more extensive Early Palaeozoic sedimentary basin within which the reservoir and source rocks were deposited. The key to the understanding of the Cambro-Ordovician play is the relative timing of oil generation compared to the Cretaceous and Tertiary inversion tectonics which influenced source burial depth, reactivated faults and reorganised migration pathways. At the present day only a limited area of the basin centre remains within the oil generating window. Modelling of the timing and distribution of source rock maturity uses input data from AFTA and fluid inclusion studies to define palaeo temperatures, shale velocity work to estimate maximum burial depth and source rock geochemistry to define kinetics and pseudo-Ro. Migration pathways are investigated through structural analysis. The majority of the discovered fields and identified exploration prospects in the Murzuk Basin involve traps associated with high angle reverse faults. Extensional faulting occurred in the Cambro-Ordovician and this was followed by repeated compressional movements during Late Silurian, Late Carboniferous, Mid Cretaceous and Tertiary, each associated with regional uplift and erosion.

• Economic and Environmental Geology
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• v.18 no.4
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• pp.331-342
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• 1985

The Dongbo tungsten-molybdenum deposits are fissure-filling veins emplaced in granites of late Cretaceous age. Integrated field, mineralogic and fluid inclusion studies were undertaken to illuminate the characters and origin of the ore deposits. Mineral paragenesis is complicated by repeated fracturing, but four distinct depositional stages can be recognized; (I) tungsten-molybdenum minerals-quartz-chlorite stage, (II) iron-oxide and sulfides-quartz stage, (III) iron -oxide-base metal sulfides-sulfosalts-quartz-carbonates stage, (IV) barren rhodochrosite-zeolite stage. Fluid inclusion studies were carried out for stage I quartz and stage III quartz, sphalerite and calcite. Fluid inclusion studies reveals highly systematic trends of homogenization temperature and salinity throughout the mineralization. Ore fluids during stage I were complex, NaCl rich brine and salinity reached values as high as 34.4 weight percent equivalent NaCl, but the later ore fluids were more dilute and reached to 9.7 weight percent equivalent NaCl during stage III. Intermittent boiling of ore fluid during stage I is indicated by the fluid inclusions in stage I quartz. Depositional temperatures and pressures during stage I range from $520^{\circ}C$ to $265^{\circ}C$and from 600 to 400 bars. Homogenization temperatures of the stage III quartz, sphalerite and calcite range from $305^{\circ}C$ to $190^{\circ}C$. Fluid inclusion data from the Dongbo mine are nearly similar to those from other hydrothermal tungsten deposits in the Kyeongsang basin. Depositional temperature and salinity of ore fluids during precipitation of tungsten-molybdenum minerals in Dongbo mine were much higher, but $CO_2$ contents were much lower than those from hydrothermal tungsten-molybdenum deposits of late Cretaceous plutonic association in central parts of Korean peninsula.

• Economic and Environmental Geology
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• v.8 no.4
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• pp.223-230
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• 1975

South Korea is divided tectonically into four segments. The Kyonggi-Ryongnam massif is composed of Precambrian schists and gneisses and consititutes a base for the succeeding formations. The Okcheon geosynclinal zone in the Kyonggi-Ryongnam massif strectches from southwest to northeast diagonally across the peninsula in a direction known as the Sinian direction. Its northeastern part is composed primarily of Paleozoic to early Mesozoic sedimentary formations and the southwestern part of the late Precambrian Okcheon metamorphic series. The Kyongsang basin occupies the southeast and southwest of the peninsula and is made up of a thick series of Cretaceous terrestrial sedimentary and andesitic rocks. A few small Tertiary basins are scattered in the eastern coastal area and in Cheju Island, and are composed of marine sedimentary and basaltic rocks. Jurassic Daebo granites intrude the Kyonggi-Ryongnam massif and the Okcheon zone in the Sinian direction, whereas late Cretaceous Bulkuksa granites are scattered randomly in the Kyongsang basin.

• The Korean Journal of Petroleum Geology
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• v.4 no.1_2 s.5
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• pp.1-11
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• 1996

Multichannel deep seismic reflection data in the Main Pass area of the northern Gulf of Mexico are interpreted in this study for the stratigraphy and the depositional history. Structural analysis of deep seismic reflection data provides new information on the locations of paleo-shelf margins and the basement. The basement occurs at about $7.5{\cal}km$ depth at the northern end of seismic line LSU-1 in the Mississippi shelf. The Jurassic and early Cretaceous shelf margins occupy approximately the same position, whereas the Oligocene shelf margin occurs about 28 km farther landward. Ten major seismic stratigraphic sequences are identified for the Mesozoic and Cenozoic sed-imentary section. Correlation of sequence boundaries defined in this study with those in other areas of the circum-Gulf region indicates that majo. regional unconformities formed at the mid-Miocene (10.5 Ma), mid-Oligocene (30 Ma), mid-Cretaceous (97 Ma), and top-Jurassic (131 Ma). Three distinct periods a.e recognized in the depositional history of the Main Pass area of the northern Gulf of Mexico: (1) shallow ma.me deposition du.ins the period from the opening of the Gulf to the mid-Cretaceous, (2) deep marine deposition in the Cretaceous to the mid-Oligocene, and (3) shallow marine deposition prevailed since the mid-Oligocene to present. A comparison of depositional rates between the Main Pass area and the Destin Dome area indicates that the northern Gulf of Mexico continental margin was initiated as a terrigenous sediment wedge province in the late Cretaceous.

• 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.

• Economic and Environmental Geology
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• v.19 no.spc
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• pp.175-191
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• 1986

The Geodo granodiorite intruded into the Joseon Supergroup is fine-grained at the marginal part, and medium-grained and more leucocratic at the central part. The Quartz monzonite porphyry intruded inte Precambrian granite and Geodo granodiorite has abundant plagioclase phenocryst. The Imog granite intruded into the Yulri Group and the Joseon Supergroup is mediumgrained biotite granite with partly pinkish feldspar phenocryst. The K/Ar ages obtained from the biotite of the Geodo granodiorite and Imog granite are Early ($111{\pm}1{\sim}107{\pm}1$ Ma) and Late ($93{\pm}1{\sim}92{\pm}1$ Ma) Cretaceous, respectively. The K/Ar sericite age of the quartz-sericite zone of the lower Jangsan quartzite occuring in the western area gave much younger age (about 170 Ma) than that of the Jangsan quartzite, that might be reset due to the regional metamorphism of the Daebo orogeny. The granitic rocks of the area are felsic to mafic, metaluminous to peraluminous, calc-alkalic (alkali-lime index${\fallingdotseq}$ 57) and I-type (magnetite-series) based on the chemical data_ And they appear to have been fractionated at the order of Geodo granodiorite, Quartz monzonite porphyry and Imog granite. In terms of mineralogy, geochemistry and K/Ar biotite age, a rock suite of monzodiorite, quartz monzodiorite and quartz monzonite-granodiorite in the Geodo stock was fractionally differentiated from a magmatic body from its margin to inward.

• Journal of the Mineralogical Society of Korea
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• v.6 no.2
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• pp.80-93
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• 1993

Jido kaolin deposits developed in the rhyolitic tuff of Cretaceous are located in the western part of Sinan-gun, Jeonranam-do. Jido kaolin deposits is predominantly composed of pyrophyllite, kaolinite and illite. On the basis of mineral assemblage Jido kaolin deposits can be divided into three alteraion zone from the center of alteration to the margin; kaolinite, kaolinite-pyrophyillite and pyrophyillite zones. Discriminant analysis show that $Al_2O_3$, $K_2O$, $Na_2O$, CaO of major elements are discriminant elements classifying kaolinite, kaolinite-pyrophyllite and pyrophyllite zones, while in case of trace elements Cr, Ni, Sc, Zn, and Zr are discriminant elements. Kaolin deposits has been formed by the hydrothermal alterations of the volcano rocks such as rhyolitic tuff and lapilli tuff, in late cretaceous. On the basis of the results of X-ray diffraction analysis, the deposits can be classified into three types of minerals assemblages; kaolinite, kaolinite-pyrophyllite and pyrophyllite zones. All the assemblages contain quartz and muscovite, but the kaolinite zone contains kaolinite, illite and chlorite, the kaolinite-pyrophyllite zone contains kaolinite, pyrophyllite and the pyrophyllite zone contains illite and pyrite.

• 한국석유지질학회:학술대회논문집
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• spring
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• pp.48-55
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• 1998

The Pohang Basin is located in Pohang City and adjacent coastal areas in the southeastern Korea. It has a sequence of 900 meters of Neogene marine sediments (Yeonil Group) while offshore basins in the East Sea, e.g., the Ulleng basin, is over 10 Km in thickness. An understanding of the marine Yeonil Group in the Pohang Basin may provide insights into the hydrocarbon potential of the offshore East Sea regions. Heulandite, smectite, dolomite, kaolinite and opal-CT are commonly found as diagenetic minerals in the Yeonil Group. Among these minerals, heulandite occurs as a main cement only in sandstones consisting of volcanic matrix, Smectite composition and diagenetic mineral facies such as heulandite and opal-CT may reflect that the Yeonil Group has undergone shallow burial, temperatures below about 60 degrees. This suggest that sandstones have experiened weak diagenetic alteration. In order to reconstruct the thermal history of the basin, apatite fission-track analysis was carried out. Aapparent apatite fission-track ages (AFTAs) exhibit a broader range of ages from 238 Ma to 27 Ma with mean track lengths in the range of $15.24\pm8.0$ micrometers, indicating that these samples had undergone significant predepositional thermal alteration. The Triassic to Cretaceous AFTAs seem In represent the timing of cooling of their sedimentary sources. Late Cretaceous mean AFTA $(79.0\pm8.0 Ma)$ on the Neogene Yeonil Group indicates that the Yeonil Group had not been buried deeper than 2km since its deposition. The organic matters of. the Pohang Basin remain in the immature stage of thermal evolution because burial depth and temperature were not sufficient enough for maturation even in the deep section of the basin.

• Economic and Environmental Geology
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• v.21 no.4
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• pp.335-348
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• 1988

The author aimed to describe the volcano-stratigraphy and petrology of the volcanic mass in the Koheung peninsula, South Cheolla province. The volcanic mass is composed of the volcanics and intrusives of late Cretaceous which extruded the Pre-cambrian metamorphic(Jirisan gneiss complex) and the early Cretaceous sedimentary(Duwon Formation) basement. The volcanic pile consists of, in ascending order, Bibongsan andesite, Koheung tuff and breccia, and Palyeongsan welded tuff, and are intruded by ring intrusives( intrusive breccia, andesite porphyry, intrusive rhyolite and fine-grained quartz-diorite) and central pluton(diorite, quartz monzodiorite, biotite granite and micrographic granite). Bibongsan andesite mainly consists of andesite tuff and lava. Koheung tuff consists of alternation of fine tuff, coarse tuff and lapilli tuff, and Palyeongsan welded tuff which overlies Koheung tuff, comprises K-feldspar and quartz phenocrysts, elongated brown fiamme, lithic fragments in matrix of devitrified brown glass shards, and mainly consists of rhyodacite to rhyolite vitric ash-flow tuff. The results of petrochemical studies of the igneous rocks suggest that the rocks were a serial differentiational products of fractional crystallization of calc-alkaline magma series. This study reveals that the volcanic mass in this area is inferred to the remnant of the resurgent cauldron, measuring 30 by 25 km in diameter. The cauldron block was lowered at least 1,000 m by ring fault displacement.

• Economic and Environmental Geology
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• v.3 no.3
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• pp.177-186
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• 1970

Bupyong lead-silver mine is located at outskirt of Inchon, a harbor city on the Yellow Sea about 40 km due west of Seoul. The geology of the area is composed of gneisses of pre-Cambrian age, rhyolite of Jurassic to Cretaceous age which extruded over the gneisses and late Cretaceous granite. Small diabasic dike is observed only in the underground. The contact plane between overlying rhyolite and underlain gneiss is sinuous and generally pitches about $30^{\circ}{\sim}40^{\circ}$ toward east. Conjugate joints and fissures are well developed in the rhyolite striking generally north-southward. Three ore bodies are being exploited and three more are under prospecting. These ore bodies range from few tons of hundred thousand to million tons in reserve. These ore bodies occur exclusively in the rhyolite along joints as network and/or desseminated type. The lower limit of ore bodies is always delineated at about 20~30m above the gneiss which might be indicative of ore genesis that has not been clearly explained so far. Two hypothesis on ore genesis could, however, be considered: firstly lithologic difference in the rhyolite might be a manifestation of different flows along which ore solution ascended and replaced along joints; secondly diabasic dike has acted as ore bringer since the dike contains considerable amount of silver, lead and zine. Ore minerals are galena and native silver accompanied by pyrite, argentite, pyragyrite and magnetite. It is believed that pyritization took place in advance to main mineralization, and ore deposit is classified as meso- to epi-thermal type.