首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   9篇
  免费   0篇
专业分类
地球物理   1篇
地质学   3篇
海洋学   3篇
自然地理   2篇
出版年
  2013年   3篇
  2012年   1篇
  2008年   3篇
  2006年   1篇
  1996年   1篇
排序方式： 共有9条查询结果，搜索用时 31 毫秒
1
1.
红透山块状硫化物矿石主要成分为黄铁矿、磁黄铁矿、黄铜矿、闪锌矿和石英、角闪石、黑云母等脉石矿物。将此矿石烘干后作为试料置于岩石三轴应力试验机,在13h内将轴压、围压和温度分步升至1276MPa、414MPa和350℃,然后在空气中自然冷却至室温。实验产物中黄铁矿、石英、长石等以脆性碎裂为主,而磁黄铁矿、黄铜矿、闪锌矿和云母等以塑性变形为主。再活化的黄铜矿、磁黄铁矿和少量闪锌矿呈脉和网脉穿插黄铁矿碎斑。实验结果表明,即使没有外来流体加入．构造动力作用所导致的流体包裹体破坏所释出的流体,就足以使成矿物质发生活化转移和再活化。  相似文献   
2.
We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth. 137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons.  相似文献   
3.
Laboratory experiments were carried out to assess the role of photochemical reactions upon the dissolution of 239 + 240pu and 241Am from marine sediment in sea water. Supplementary information was obtained by comparing their behaviour with that of 54Mn under similar experimental conditions. Irradiation from natural sunlight resulted in more than a ten-fold increase in the extent of 239 + 240Pu desorption relative to that observed in the dark. Remobilisation of 54Mn from sediment was also enhanced by natural sunlight, albeit to a lesser extent than 239 + 240Pu, whilst the behaviour of 241Am was largely unaffected. Data for concentrations of dissolved 239 + 240Pu(IV) and 239 + 240Pu(V) species showed that only the oxidised form was significantly affected by irradiation, indicating remobilisation occurs as a result of photooxidation reactions. Further experiments were carried out using artificial light sources to establish the influence of wavelength. Data from these investigations indicated 239 + 240Pu photooxidation (hence desorption) was a function of both light intensity and wavelength. Remobilisation decreased concomitant with light intensity but increased as the wavelength decreased. Similar trends were observed for photoreduction of 54Mn, although differences were less pronounced than those observed for 239 + 240Pu.  相似文献   
4.
Abstract

Concerns about the potential adverse effects of Spartina invasion on New Zealand estuaries, such as habitat loss and degradation, have led to herbicide use to control its spread. An experiment was conducted in the Manukau Harbour (New Zealand) to determine sediment remobilisation rates (?E) from herbicide‐treated S. anglica patches. Paired treatment and control patches (≤25 m diam.) were monitored at two sites 500 m apart with different wave exposures. Above‐ (AGB) and below‐ground (BGB) biomass decomposition and AE were determined from repeat surveys over c. 2.5 years. Work done by waves (W), which integrates wave‐energy dissipation at the bed over time, was used as a surrogate measure of sediment transport potential. Complete AGB loss occurred in both treated patches within 3 months of initial herbicide application, whereas BGB (a matrix of roots and rhizomes) persisted much longer. An exponential decay model (r 2 = 0.6) fitted to the site‐two treatment data predicted an c. 85% reduction in BGB after 5 years, whereas the BGB changes for the larger and more heterogeneous site‐one treatment were more complex. BGB was a better predictor of average bed elevation than AGB in multiple regression models and, although bed elevation decreased through time and with waves, BGB was positively related to bed elevation at both sites. AE was similar for both treatment patches (c. 0.05 and c. 0.06 m yr‐1, P < 0.001, r2 ≥ 0.97) and complete sediment loss was predicted to occur within 6–10 years. The site‐one control patch accumulated sediment (0.01 m yr‐1 , P < 0.001, r 2 = 0.81) whereas the more wave‐exposed site‐two control eroded (0.01 m yr‐1, P = 0.0017, r 2 = 0.61). The potential for adverse sediment effects resulting from Spartina control at wave‐exposed sites will be minimal if the treated areas are small relative to the size of the estuary.  相似文献   
5.
Abstract

Surface sediment samples (60 μm‐2 mm, and < 60 μm fractions) from the Waiwhetu Stream, Lower Hutt City, New Zealand, were leached with dilute HCl to remove the mobile heavy‐metal fraction. Cd, Cr, Cu, Pb, Zn, Al, Fe, and Mn analyses of the leachates show that sediments of the upper reaches area of the stream are generally uncontaminated. In contrast, sediments in the lower reaches area are highly contaminated, despite clean‐up measures in the late 1970s. Lead and Zn are the most significantly enriched metals with concentrations over 1000 mg kg?1 adjacent to some drains. In the polluted zone, metals originate from either upward remobilisation from underlying sediment (contaminated in the early 1960s and 70s) or more recent industrial spillages. Similar trends exhibited by Cd, Cu, Cr, Zn, Pb, and Al indicate that a proportion of the metal enrichment downstream probably results from a naturally higher clay content of sediments near the mouth of the stream. Fe and Mn show reverse trends to the other metals, indicating that a high proportion of these two metals occurs in substrate different to that of the other metals. The orange brick‐coloured sediments of the upper reaches of the stream indicate oxides upstream; the black sediments in the lower reaches indicate sulphides downstream.  相似文献   
6.
We conducted experiments to simulate sulfide remobilisation from sulfide ore. The starting material was from the Hongtoushan massive sulfide deposit, NE China, and is composed of pyrite, pyrrhotite, chalcopyrite, sphalerite, quartz, and silicate minerals. The ore was immersed in a solution of 20 wt.% NaCl for 260 h, and then was mounted in a Changjiang 500 triaxial rock stress machine. After the experiments were performed for 13 h at temperatures of 362, 464, 556 and 682°C, with corresponding confining and axial pressures, the samples were cooled at room temperatures. Our results from all the runs indicate that sulfides can be remobilised both mechanically and chemically, and that remobilisation is enhanced at higher temperatures. Mechanical remobilisation can only take place over limited distances and results in minor differentiation between various sulfide minerals. Distant external remobilisation to form new orebodies is most likely caused by chemical remobilisation. In contrast to plastically deformed areas, space resulting from cataclastic deformation could provide conduits for fluid transport and space for metal precipitation. Remobilised iron sulfides will precipitate as pyrrhotite at high temperatures, but as pyrite when temperature decreases. Furthermore, chalcopyrite is more easily remobilised than sphalerite under the conditions of the present experiments. Remobilisation accompanying deformation and metamorphism may add epigenetic features to syngenetic deposits.  相似文献   
7.
Mercury, with its reactive forms being the most deleterious for the trophic chains, has been identified as a major pollutant in a few confined bodies of the coastal zone. Due to feeding, burrowing, and bioirrigation activities, infauna are known to play a crucial role in the biogeochemical processes of contaminants. The main goal of the present study is to evaluate the effects of Hediste diversicolor bioturbation on mercury fluxes from estuarine sediments in a mesocosms laboratory experiment. Additionally, an attempt was made to establish a relationship between the amount of remobilised mercury to the water column and the degree of contamination of the sediments using a mercury contamination gradient. The present experiment demonstrated that the bioturbation activity caused by the gallery-diffuser H. diversicolor did not influence the remobilisation of mercury (in dissolved reactive forms) from the sediment to the water column. The concentration of dissolved reactive mercury in the water column also did not reflect the degree of contamination in the sediments. The results obtained were in accordance with the sediment characteristics of the Mondego Estuary and Ria de Aveiro (Portugal), since they are very rich in organic matter content, iron/manganese total and hydrous oxides. These physicochemical characteristics of the sediments may partially justify the retention of mercury by these systems, even when they are subjected to bioturbation. In conclusion, sediments with high organic matter content and a high concentration of iron/manganese hydrous oxides allowed for efficient retention of mercury, and the bioturbation process did not seem to affect the system. Another conclusion from this study is that the remobilisation of mercury by bioturbation to the water column is not a fast process, requiring more than 24h. This study constitutes an important work in the area of the effects of bioturbation on mercury remobilisation. Considering the toxicity of mercury for the biota, it is essential to evaluate the real magnitude of mercury processes occurring in estuarine systems in order to obtain essential information on metal behaviour.  相似文献   
8.
The Early‐Middle Proterozoic Broken Hill Block contains three types of W occurrences, which show close stratigraphic control. All three types occur within a relatively narrow stratigraphic interval (the ‘Mine Sequence’ Suite of Stevens et al., 1980) comprising a highly variable group of metamorphosed silicic and mafic volcanics, clastic sediments, and exhalative and chemical sediments containing base metals. The first type includes occurrences of W and base metals in bedded calc‐silicate rocks. In the second type, W occurs in layered to non‐layered calcsilicate rocks associated with amphibolite; these are intimately associated in a narrow stratigraphic interval containing abundant, small, Broken Hill type deposits. The third type comprises stratabound, W‐bearing pegmatites, which have been remobilised from quartz‐feldspar‐biotite gneiss and bedded quartz‐tourmaline rocks. Tungsten has been mined only from the third type and only in small quantities. The three types of tungsten deposits show a close spatial relationship with stratiform and stratabound Pb‐Zn mineralisation, including the Broken Hill type. The Pb‐Zn and W deposits are inferred to be genetically related.  相似文献   
9.
Soil redistribution studies are important, especially in water supply catchments, because the rate at which denudation is occurring has implications for offsite water quality. However, the extent to which soil is redistributed within the landscape can be difficult to determine. This challenge can be overcome using fallout caesium-137 (137Cs). This paper describes the rates of soil loss and remobilisation in two sub-catchments within the Sydney Basin region, namely Kembla and Kentish Creeks, which drain to the Cordeaux reservoir. The total inventories of 137Cs in catchment soils were determined, a 137Cs-regression equation and a theoretical diffusion and migration model were used to established relationships between 137Cs inventories and the rates of soil loss. These relationships revealed relatively low occurrence of soil loss in Kentish Creek, but two slopes in the Kembla Creek sub-catchment had losses that appear to be moderate. However, there was no clear evidence to suggest whether slopes in upper and lower reaches of catchments had specific patterns of soil remobilisation. Qualitative categorisation of the slope elements using a 137Cs-sediment hillslope model can be a useful sentinel for land users and decision makers even if absolute rates of soil loss or gain are not certain. The findings suggest that sediments mobilised in the study sub-catchments are not likely to impact significantly on the water quality in the Cordeaux reservoir.  相似文献   
1
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号