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81.
Sang Hoon CHOI 《Resource Geology》1998,48(3):171-182
Abstract: The Daejang mine is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into four stages (stages I, II, III and IV) by major tectonic fracturing. Stages I, III and IV are economically barren. Stage II, at which the precipitation of major ore minerals occurred, is further divided into three substages with paragenetic time based on minor fractures and discernible mineral assemblages: substage IIa, marked by deposition of quartz and Fe–sulfides; substage IIb, by introduction of base-metal sulfides within carbonates and some quartz; substage IIc, by quartz and carbonates with various sulfosalts. Fluid inclusion data indicate a complex geochemical evolution of hydrothermal fluids. Both CO2–rich and H2O–rich fluids were trapped in fluid inclusions at stage I and substage IIa. It is suggested that a compositionally heterogeneous fluid was formed by fluid boiling and CO2 immiscibility at temperatures of about 400° to 300°C. Composite lodes of base-metal sul–fides, carbonates and quartz at substage IIb were deposited in open spaces created by fracturing. The fracturing event prompted rapid decreases in pressure and temperature of residual fluids and resulted in retrograde fluid boiling at about 200 bars and 300°–250°C during substage IIb. The progressive loss of CO2 by CO2 effervescence and retrograde boiling from substage IIa and IIb fluids resulted in pH increase and related increase in carbonate activity, causing deposition of abundant carbonates. The change in pH also caused the decrease of stability of hydrogen sulfide with Cu, Zn and Pb chloride complexes (as main transporting agents at Daejang) and resulted in the pricipitation of base-metal minerals. Deposition of Ag– and Sb-bearing sul–fides and sulfosalts of substage IIc occurred at temperatures of about 250° to 150°C from a dominantly aqueous fluid with low salinity (down to 3. 0 equiv. wt % NaCl). At this substage, aqueous fluid formed by mixing with cooler and less saline meteoric groundwater. There is a systematic decrease in caculated δ18Owater values with the mineralization stage (and decreasing temperature) in the Daejang hydrothermal system, from values of about 11% for stage I, through about 4% for stages II and III, to about –3 per mil for stage IV. The result of stable isotope and fluid inclusion studies are interpreted to indicate progressive less evolved and/or unexchanged meteoric water influx of an early hydrothermal system formed by highly evolved meteoric waters. 相似文献
82.
Abstract Ultramafic xenoliths in alkali basalts from Jeju Island, Korea, are mostly spinel lherzolites with subordinate amounts of spinel harzburgites and pyroxenites. The compositions of major oxides and compatible to moderately incompatible elements of the Jeju peridotite xenoliths suggest that they are residues after various extents of melting. The estimated degrees of partial melting from compositionally homogeneous and unfractionated mantle to form the residual xenoliths reach 30%. However, their complex patterns of chondrite-normalized rare earth element, from light rare earth element (LREE)-depleted through spoon-shaped to LREE-enriched, reflect an additional process. Metasomatism by a small amount of melt/fluid enriched in LREE followed the former melt removal, which resulted in the enrichment of the incompatible trace elements. Sr and Nd isotopic ratios of the Jeju xenoliths display a wide scatter from depleted mid-oceanic ridge basalt (MORB)-like to near bulk-earth estimates along the MORB–oceanic island basalt (OIB) mantle array. The varieties in modal proportions of minerals, (La/Yb)N ratio and Sr-Nd isotopes for the xenoliths demonstrate that the lithospheric mantle beneath Jeju Island is heterogeneous. The heterogeneity is a probable result of its long-term growth and enrichment history. 相似文献
83.
Jin-Yong Gui Jian-Hu Gao Xue-Shan Yong Sheng-Jun Li Bin-Yang Liu Wan-Jin Zhao 《应用地球物理》2015,12(4):523-532
Variation of reservoir physical properties can cause changes in its elastic parameters. However, this is not a simple linear relation. Furthermore, the lack of observations, data overlap, noise interference, and idealized models increases the uncertainties of the inversion result. Thus, we propose an inversion method that is different from traditional statistical rock physics modeling. First, we use deterministic and stochastic rock physics models considering the uncertainties of elastic parameters obtained by prestack seismic inversion and introduce weighting coefficients to establish a weighted statistical relation between reservoir and elastic parameters. Second, based on the weighted statistical relation, we use Markov chain Monte Carlo simulations to generate the random joint distribution space of reservoir and elastic parameters that serves as a sample solution space of an objective function. Finally, we propose a fast solution criterion to maximize the posterior probability density and obtain reservoir parameters. The method has high efficiency and application potential. 相似文献
84.
85.
Late Cenozoic alkali basalts in the Ganseong area of South Korea contain abundant ultramafic xenoliths and clinopyroxene megacrysts. Anhydrous clinopyroxene‐rich wehrlite–clinopyroxenites make up the majority of the xenolith population and range from wehrlite through olivine clinopyroxenite to clinopyroxenite. This study investigates the petrogenesis of wehrlite–clinopyroxenite xenoliths and clinopyroxene megacrysts on the basis of petrography and mineral and whole‐rock chemistry. Observations such as an absence of carbonate or apatite, high Ti/Eu ratio, and clinopyroxene‐dominated mineralogy lead us to rule out peridotite–melt reactions as the origin of the Ganseong wehrlites– olivine clinopyroxenites. The whole‐rock compositions (e.g. high abundance of CaO at a given MgO content and low abundance of incompatible elements, such as U, K, P, and Ti compared with mafic melts) indicate that the pyroxenites do not represent crystallized magma itself, but are rather cumulates with a small amount of residual liquid. Anhydrous and orthopyroxene‐free mineral assemblages, crystallization sequence of olivine→clinopyroxene→plagioclase, and mineral chemistries (e.g. low Cr# and high TiO2 abundances in spinels and high TiO2 and Na2O abundances in clinopyroxenes at a given Mg#) suggest that relatively anhydrous intraplate alkaline basalt is the most likely candidate for the parent magma. Texture and compositions of the clinopyroxene megacrysts preclude a cognate origin via high‐pressure crystallization of the host magma. The clinopyroxene megacrysts occupy the Fe‐rich end of the compositional trends defined by wehrlite–pyroxenite clinopyroxenes. Progressive decreases in Mg# and an absence of significant compositional gaps between pyroxenite xenoliths and clinopyroxene megacrysts indicate fractionation and differentiation of a similar parental magma. We suggest that the clinopyroxene megacrysts represent fragments of pegmatitic clinopyroxenites crystallized from more advanced fractionation stages of the evolution of a series of magmatic liquids formed Ganseong wehrlite–clinopyroxenites. 相似文献
86.
Submarine groundwater discharge into the coast revealed by water chemistry of man-made undersea liquefied petroleum gas cavern 总被引:1,自引:0,他引:1
The occurrence of submarine groundwater discharge (SGD) as well as its supply of many nutrients and metals to coastal seawaters is now generally known. However, previous studies have focused on the chemical and radiological analysis of groundwater, surface seawater, shallow marine sediments and their pore waters, as well as the measurement of upward flow through the marine sediments, as end members of the discharge process. In this study, chemical and isotopic analysis results of marine subsurface waters are reported. These were obtained from deep boreholes of an undersea liquefied petroleum gas (LPG) storage cavern, located about 8 km off the western coast of Korea. The cavern is about 130–150 m below the sea bottom, which is covered by a 4.8–19.5 m silty clay stratum. An isotopic composition (δ2H and δ18O) of the marine subsurface waters falls on a mixing line between terrestrial groundwater and seawater. Vertical EC profiling at the cavern boreholes revealed the existence of a fresh water zone. An increase in the contents of ferrous iron and manganese and a decrease in levels of nitrate, bicarbonate and cavern seepage were recorded in August 2006, indicating a decreased submarine groundwater flux originating from land, mainly caused by an elevated cavern gas pressure. It is suggested in this study that the main source of fresh waters in the man-made undersea cavern is the submarine groundwater discharge mainly originating from the land. 相似文献
87.
A simulation of suspended sediment movement relating to tidal and wave forcing during a winter monsoon in November 1983 in the Huanghai and East China Seas continental shelf is attempted by using the model describing the cohesive/non-cohesive sediment resuspension generated by interactions between currents and waves.model simulation showed that sediment concentration was increased by resuspension at shallow depths during the strong storm conditions due to high bottom stress interacted between currents and waves. This result is in general agreement with observations in horizontal distribution of suspended sediment distribution.At three current meter mooring positions off the southern Shandong Peninsula resuspension occurred only at a depth of 22m,nearest coastal position and at deeper parts at depths of 51 and 80m wave-current interaction effects were not significant. It has shown that the present model simulation demonstrated the capability of reproduction of suspended sediment movement under wintertime extreme event reasonably well. 相似文献
88.
National scale evaluation of groundwater chemistry in Korea coastal aquifers: evidences of seawater intrusion 总被引:3,自引:2,他引:1
Youngyun Park Jin-Yong Lee Jeong-Hee Kim Sung-Ho Song 《Environmental Earth Sciences》2012,66(3):707-718
Pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of Korea. Therefore, seawater intrusion monitoring stations were installed in eastern, western, and southern coastal areas and have been operated since 1998. In this study, groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated. Groundwater was classified into fresh (<1,500 μS/cm), brackish (1,500–3,000 μS/cm), and saline (>3,000 μS/cm) according to EC levels. Among groundwater samples (n = 233), 56, 7, and 37% were classified as the fresh, brackish, and saline, respectively. The major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater. The enrichment of Na+ and Cl− was especially noticeable due to seawater intrusion. Thus, the brackish and saline groundwaters were classified as Ca–Cl and Na–Cl types, while the fresh groundwater was classified as Na–HCO3 and Ca–HCO3 types. The groundwater included in the Na–Cl types indicated the effects of seawater mixing. Ca2+, Mg2+, Na+, K+, SO4 2−, and Br− showed good correlations with Cl− of over r = 0.624. Of these components, the strong correlations of Mg2+, SO4 2−, and Br− with Cl− (r ≥ 0.823) indicated a distinct mixing between fresh groundwater and seawater. The Ca/Cl and HCO3/Cl ratios of the groundwaters gradually decreased and approached those of seawater. The Mg/Cl, Na/Cl, K/Cl, SO4/Cl, and Br/Cl ratios of the groundwaters gradually decreased, and were similar to or lower than those of seawater, indicating that Mg2+, Na+, K+, SO4 2−, and Br−, as well as Cl− in the saline groundwater can be enriched by seawater mixing, while Ca2+ and HCO3 − are mainly released by weathering processes. The influence of seawater intrusion was evaluated using threshold values of Cl− and Br−, which were estimated as 80.5 and 0.54 mg/L, respectively. According to these criteria, 41–50% of the groundwaters were affected by seawater mixing. 相似文献
89.
This study revealed a high positive correlation between rainfall in Korea during September and the trade wind (TW)/Arctic Oscillation (AO) index in May that combines two climate factors, low-level TWs and the AO. This correlation was identified on the basis of the difference in the 850 hPa streamline analysis between the positive and negative phases selected using the combined TW/AO index. In May, the spatial pattern of the anomalous pressure systems is similar to that in the positive AO phase. These anomalous pressure systems continue in June to August (JJA) and September, but the overall spatial distribution shifts a little to the south. Particularly in September, a huge anomalous anticyclone centered over the southeast seas of Japan strengthens in most of the western north Pacific region and supplies a large volume of warm and humid air to the region near Korea. This characteristic is confirmed by the facts that during the positive TW/AO phase, the subtropical western north Pacific high (SWNPH) is more developed to the north and that the continuous positioning of the upper troposphere jet over Korea from May to September strengthens the anomalous upward flow, bringing warm and humid air to all layers. These factors contribute to increasing September rainfall in Korea during the positive TW/AO phase. Because the SWNPH develops more to the north in the positive phase, tropical cyclones tend to make landfall in Korea frequently, which also plays a positive role in increasing September rainfall in Korea.The above features are also reflected by the differences in average rainfall between the six years that had the highest May Ni o 3.4 indices (El Ni o phase) and the six years that had the lowest May Ni o 3.4 indices (La Ni a phase). 相似文献
90.
An examination was carried out of the encrusting materials on the seepage removal pumps in a bottom sump of an undersea liquefied petroleum gas (LPG) cavern. The studied cavern, constructed at 8 km off the western coast of Korea, facing the Yellow Sea, is at 130–150 m below the seabed. Since the first filling of the LPG into the cavern, it has suffered from the unexpected problem of a thick encrustation of unknown materials on the seepage removal pumps of the cavern. The XRD and XRF analyses revealed that the encrustation materials were mainly iron (hydro)oxides and carbonate mineral (aragonite). Based on the geological setting below the cavern site, it was inferred that iron oxides found in the Pleistocene sandy sediment and the Precambrian gneiss might be supplying ferrous iron to the cavern waters under an anaerobic condition, evidenced by low dissolved oxygen and negative redox potential in the cavern water. A significant change in the hydraulic condition near the pump intake and mixing the cavern water with oxic waters supplied through re-circulated seawater and terrestrial groundwater discharge, would precipitate the dissolved iron. Precipitation of the carbonate mineral is thought to have occurred due to over-saturation of calcium and bicarbonate, which may have resulted from the dissolution of cement grouting materials used during the undersea cavern construction and submarine groundwater discharge (SGD). This study reports the iron and carbonate precipitation in the man-made undersea cavern, which is affected by the surrounding hydrogeological condition and the SGD. 相似文献