排序方式： 共有13条查询结果，搜索用时 312 毫秒
1.
Ashworth Luisa Kinnaird Judith Ann Nex Paul Andrew Martin Erasmus Rudolph Marthinus Przybyłowicz Wojciech Józef 《Mineralogy and Petrology》2018,112(6):753-765
Mineralogy and Petrology - Mineralized NYF and LCT pegmatites occur throughout the northeast-trending Neoproterozoic Damara Belt, Namibia. Mineralization in the pegmatites varies geographically,... 相似文献
2.
Some of the world’s deepest goldmines operate below dolomitic karst aquifers in the Far West Rand (FWR) goldfield, South Africa. Associated impacts include the continuous dewatering of karst aquifers for over six decades and irreversible changes of the hydrogeological setting. Affecting an area of approximately 400 km2 by drawing down the water table up to 700 m, these impacts, and the large amounts of data generated in the process, are used as unique research opportunities to better understand the complex karst hydrology. The focus of this study is on predicting final water table elevations in rewatered aquifers after mining ceases taking the fact that mines hydraulically linked previously disconnected aquifers into account. While part 1 of this series develops the conceptual model, this second part utilises large sets of pertinent data to calculate actual flow rates for predicting the fate of dried up springs after mine closure. Following a Darcy-based approach first applied by Swart et al. (Environ Geol 44:751–770, 2003a) it is not only predicted that the springs will flow again but also shown that linear relationships exist between flow rates through a combined system of karst-fractured aquifers overlying the mine void and the associated hydraulic head driving them. This suggests that—at this scale—porous media-based equations can be meaningfully used to predict flow in non-porous media. 相似文献
3.
Dry ore dust pollution decreased the hatching success of fowl eggs from 76% in the control to 57% when manganese ore dust and 54% when iron ore dust were used. Daily wetting of eggs aggravated the ore dust effect. When eggs were covered with ore dust, the heat exchange properties of eggs exposed to direct sunlight were significantly changed. Manganese and iron ore dust covered eggs heated and cooled at a significantly faster rates than the controls. The interior uppermost area may reach a temperature of 54°C after 60 minutes in the sun. Manganese ore dust covered brown eggs were the most affected and white eggs the least. Ore dust pollution therefore poses a threat to the hatching success of bird eggs. 相似文献
4.
T.S Mccarthy C.A Lee H.W Fesq E.J.D Kable C.S Erasmus 《Geochimica et cosmochimica acta》1984,48(5):1005-1019
A suite of ultramafic and mafic rocks from the lower, critical and lower portion of the main zones of the Bushveld Complex has been analysed for Th, Cs, Zr, Ni, Cr and Au by INAA and XRF spectrometry. The incompatible elements Th, Cs, and Zr correlate positively, and show a gradual upward increase in abundance. Assuming constant average proportion of intercumulus material, this upward increase implies that the zones of the Complex studied represent crystallization of a single magma type some 3600 m thick. Pyroxenites dominate the lower portion of the section studied and their Ni content shows an initial rapid decrease from 850 ppm in the lowermost rocks, to around 500 ppm, with considerable scatter. This distribution is most likely to have resulted from bottom crystallization with superimposed convective overturn near the transient floor of the chamber. Gold abundances are generally higher in chromitites, and correlate positively with Ni, indicating the presence of significant amounts of cumulus immiscible sulphide. In the silicate rocks, Au does not correlate with any of the analysed elements, and it is concluded that Au was trapped in small quantities of immiscible sulphide which precipitated continuously during crystallization. There is an upward increase in the amount of cumulus immiscible sulphide, indicating a progressive increase in sulphur solubility in the magma. 相似文献
5.
S. Farrell‐Turner W. U. Reimold M. Nieuwoudt R. M. Erasmus 《Meteoritics & planetary science》2005,40(9-10):1311-1327
Abstract— Previous Raman investigations on experimentally shocked ingle‐crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock‐metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64–92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm?1. Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm?1 band with increased shock pressure in the shocked Åheim samples above 45 GPa and, to a lesser extent, for the 856 cm?1 band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (9–20 cm?1) than those of olivine in the shocked dunite samples (7–12 cm?1). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm?1 was identified in the Raman spectra of the unshocked Mooihoek dunite and the Åheim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm?1 in all the spectra of the 59 GPa Åheim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine. 相似文献
6.
7.
Induced moult has been suggested as a technique for rehabilitating oiled seabirds. An oiled jackass penguin underwent natural moult in captivity. Analyses of oil extracted from premoult and postmoult feathers indicate little qualitative difference, with significant amounts of oil transferred from premoult to postmoult feathers. Inducing moult, therefore does not appear to be viable for cleaning oiled seabirds. 相似文献
8.
Some of the world’s deepest goldmines are located in the Far West Rand (FWR) goldfield operating below of up to 1.2-km-thick dolomites hosting some of the largest karst aquifers in South Africa. Associated impacts include the dewatering of the overlying karst aquifers as well as linking previously disconnected compartments by mining through aquicludes (dykes). The focus of the study is on predicting groundwater balances in re-watered aquifers after mining ceases as this will determine whether or not associated karst springs that dried-up due to dewatering will ever flow again. Critically revisiting, Swart et al. (Environ Geol 44:751–770, 2003a) who predict that all springs will flow again, this study uses significantly larger data sets and modified assumptions to increase the robustness of findings as the question is crucial for post-closure development. As a first of two papers, this part develops a conceptual model on the mega-compartment concept that predicts a flat water table across all linked compartments that would leave the springs dry. The model identifies the ratio between inflowing surface water (recharge) and underground water losses to downstream compartments via mined-through dykes (‘inter-compartmental groundwater flow’, IGF) as a key factor governing the elevation of the post-mining water table, creating the base for part 2, where the IGF and the post-mining water tables are determined using unique large data sets that have not been evaluated before. 相似文献
9.
Klemens Link Daniel Koehn Matthias G. Barth John V. Tiberindwa Erasmus Barifaijo Kevin Aanyu Stephen F. Foley 《International Journal of Earth Sciences》2010,99(7):1559-1573
Western Uganda is a key region for understanding the development of the western branch of the East African rift system and
its interaction with pre-existing cratonic lithosphere. It is also the site of the topographically anomalous Rwenzori Mountains,
which attain altitudes of >5000 m within the rift. New structural and geochronological data indicate that western Uganda south
and east of the Rwenzori Mountains consists of a WSW to ENE trending fold and thrust belt emplaced by thick-skinned tectonics
that thrust several slices of Proterozoic and Archaean units onto the craton from the south. The presence of Archaean units
within the thrust stack is supported by new Laser-ICP-MS U–Pb age determinations (2637–2584 Ma) on zircons from the Rwenzori
foothills. Repetition of the Paleoproterozoic units is confirmed by mapping the internal stratigraphy where a basal quartzite
can be used as marker layer, and discrete thrust units show distinct metamorphic grades. The thrust belt is partially unconformably
covered by a Neoproterozoic nappe correlated with the Kibaran orogenic belt. Even though conglomerates mark the bottom of
the Kibaran unit, intensive brittle fault zones and pseudotachylites disprove an autochthonous position. The composition of
volcanics in the Toro-Ankole field of western Uganda can be explained by the persistence of a cratonic lithosphere root beneath
the northwardly thrusted Archaean and Palaeoproterozoic rocks of westernmost Uganda. Volcanic geochemistry indicates thinning
of the lithosphere from >140 km beneath Toro-Ankole to ca. 80 km beneath the Virunga volcanic field about 150 km to the south.
We conclude that the western branch of the East African rift system was initiated in an area of thinner lithosphere with Palaeoproterozoic
cover in the Virunga area and has propagated northwards where it now abuts against thick cratonic lithosphere covered by a
thrust belt consisting of gneisses, metasediments and metavolcanics of Neoarchaean to Proterozoic age. 相似文献
10.
The Diep River estuary, a small estuary in suburban Cape Town, South Africa, has been subject to disturbance for centuries. Several earlier studies have documented conditions in the system, providing baselines against which to measure more recent changes. This study: (i) describes major physical and hydrological changes that have occurred within this estuary; (ii) documents faunistic changes subsequent to earlier biological surveys; and (iii) provides an up-to-date faunal list. Salinity measurements and both invertebrate and fish samples were taken at five stations along the estuary in summer and winter 2014. A census of sandprawn Callichirus kraussi densities was also undertaken to compare with earlier surveys. Developments within the Diep River catchment and estuary have resulted in extensive changes in flow and salinity regimes, causing marked reductions in summer salinity levels, changes in frequency of mouth closure, and deteriorations in water quality. These have resulted in major changes in faunal composition and distribution, including an increase in numbers of non-indigenous species. Surveys in the early 1950s recorded 47 invertebrate species, whereas only 23 were found in 1974. A total of 23 species were again recorded in 2014, but these included several freshwater forms not previously reported, which had entered the system due to lowered salinity values, as well as new alien introductions. Only six of the 69 taxa recorded were reported by all three surveys. There have been substantial declines in sandprawn abundance, from 40 million in 1998 to just over 12 million in 2014. In all, 12 fish species were recorded in the 1950s, nine in 1974, but only five in 2014, including the newly detected invasive mosquito fish Gambusia affinis and the translocated tilapia Tilapia sparrmanii. Thus, only three of the original native fish species remain. Contrary to these losses, the present bird fauna appear to be more abundant and diverse than previously. Regular monitoring is recommended to obtain a clearer understanding of ongoing changes, and major management interventions will be needed if further degradation is to be prevented. 相似文献