Trace element geochemistry by laser ablation ICP-MS of micas associated with Ta mineralization in the Tanco pegmatite,Manitoba, Canada   总被引：3，自引：0，他引：3  

Marieke Van Lichtervelde  Michel Grégoire  Robert L. Linnen  Didier Béziat  Stefano Salvi 《Contributions to Mineralogy and Petrology》2008,155(6):791-806

In the Tanco pegmatite, one of the world’s major Ta deposits, tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite. Micas are common in most of the pegmatite units and are intimately associated with the successive stages of Ta mineralization, from the wall zone to the central zones where micaceous replacement is pervasive. Different generations of micas, both primary and secondary, associated with Ta oxides, were selected for electron microprobe and laser ablation ICP-MS investigation. Their chemical trends are used to constrain the magmatic versus hydrothermal processes that played a role in their crystallization and their associated Ta mineralization. Micas range from dioctahedral muscovite to trioctahedral lepidolite through Al↔Li substitution. Unexpectedly, the most evolved compositions (low K/Rb ratios and high Li contents) occur in the wall zone; they are interpreted to reflect nonequilibrium crystallization from an undercooled melt, with or without boundary layer effects. In the central zones, the fine-grained mica–quartz assemblage hosts some coarser-grained Li-muscovite, which has the highest Ta contents (up to 400 ppm). These Li–F–a-rich micas are interpreted to originate from a magmatic metasomatic event, which was also at the origin of the MQM-style Ta mineralization at Tanco. However, the Li–Ta-poor, muscovite end-member compositions of fine-grained alteration micas suggest crystallization from an aqueous fluid, during a metasomatic (hydrothermal) event involving late pegmatitic fluids. The low Ta concentrations (around 50 ppm) of this fine-grained muscovite suggest that this fluid transported at least small amounts of Ta.  相似文献   

Clay mineral distributions in and around the Mississippi River watershed and Northern Gulf of Mexico: sources and transport patterns     

T. Sionneau  V. Bout-Roumazeilles  P.E. Biscaye  B. Van Vliet-Lanoe  A. Bory   《Quaternary Science Reviews》2008,27(17-18):1740-1751

Maps of the distributions of the four major clay minerals (smectite, illite, kaolinite and chlorite) in and around the Mississippi River drainage basin and in the Northern Gulf of Mexico have been produced using newly acquired data from erodible/alluvial terrestrial sediments and marine surface sediments, as well as from previously published data. East of the Rockies, North America can be divided into four, large, clay-mineral provinces: (1) the north-western Mississippi River watershed (smectite rich), (2) the Great Lakes area and eastern Mississippi River watershed (illite and chlorite rich), (3) the south-eastern United States (kaolinite rich) and (4) the Brazos River and south-western Mississippi River watersheds (illite and kaolinite rich). The clay mineral distributions in surface sediments of the present-day Gulf of Mexico are strongly influenced by three main factors: (1) by relative fluvial contributions: the Mississippi River delivers the bulk of the clay input to the Northern Gulf of Mexico whereas the Apalachicola, Mobile, Brazos and Rio Grande rivers inputs have more local influences; (2) by differential settling of various clay mineral species, which is identified for the first time in Northern Gulf of Mexico sediments; and (3) by oceanic current transport: the Gulf of Mexico surface and subsurface circulation distributes the clay-rich sediments from river mouth sources throughout the Northern Gulf of Mexico.  相似文献   

Employment in Cape Town’s lodging sector: opportunities, skills requirements, employee aspirations and transformation     

Kudzayi Chitiyo Maumbe  Laeticia J. Van Wyk 《GeoJournal》2008,73(2):117-132

Since the attainment of democracy in 1994 one of the major concerns of the South African government has been to address the social and economic injustices that characterised the apartheid regime. With tourism on the rise in South Africa and international arrivals growing at a rate almost triple the global rate, the tourism industry has been identified as one of the important industries to drive the transformation agenda. This study sought to assess the employment situation in Cape Town’s lodging sector, identify the existing types of jobs and skills requirements of the sector, determine career aspirations of and skills development needs for lodging sector employees as well as asses the state of transformation. Study findings showed that the lodging sector is labour intensive, requires low academic skill, and offers low paying employment following the findings that about a quarter of the respondents indicated that their jobs didn’t require any formal qualification, the average working day was 9.2 h and 52% earned below R3,500 a month. The study showed significant differences in income based on race. White employees earned significantly more than their black and coloured counterparts. However, white employees working as general labour were also significantly more qualified than their black and coloured counterparts. There was a significant positive relationship between income and length of service for white employees, but the same wasn’t true for black and coloured employees. There was a significant negative relationship between length of service and academic qualifications for black employees implying that black people’s length of service for one employer decreases as they become more academically qualified. Also significant was skills development opportunities based on gender. Significantly more females than males had attended on-the-job training programs.  相似文献   

Arsenic mobilisation in a new well field for drinking water production along the Red River,Nam Du,Hanoi     

Jenny Norrman  Charlotte J. Sparrenbom  Michael Berg  Dang Duc Nhan  Pham Quy Nhan  Håkan Rosqvist  Gunnar Jacks  Emma Sigvardsson  David Baric  Johanna Moreskog  Peter Harms-Ringdahl  Nguyen Van Hoan 《Applied Geochemistry》2008

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Multi-objective, multiple participant decision support for water management in the Andarax catchment, Almeria     

N. Van Cauwenbergh  D. Pinte  A. Tilmant  I. Frances  A. Pulido-Bosch  M. Vanclooster 《Environmental Geology》2008,54(3):479-489

Water management in the Andarax river basin (Almeria, Spain) is a multi-objective, multi-participant, long-term decision-making problem that faces several challenges. Adequate water allocation needs informed decisions to meet increasing socio-economic demands while respecting the environmental integrity of this basin. Key players in the Andarax water sector include the municipality of Almeria, the irrigators involved in the intensive greenhouse agricultural sector, and booming second residences. A decision support system (DSS) is developed to rank different sustainable planning and management alternatives according to their socio-economic and environmental performance. The DSS is intimately linked to sustainability indicators and is designed through a public participation process. Indicators are linked to criteria reflecting stakeholders concerns in the 2005 field survey, such as fulfilling water demand, water price, technical and economical efficiency, social and environmental impacts. Indicators can be partly quantified after simulating the operation of the groundwater reservoir over a 20-year planning period and partly through a parallel expert evaluation process. To predict the impact of future water demand in the catchment, several development scenarios are designed to be evaluated in the DSS. The successive multi-criteria analysis of the performance indicators permits the ranking of the different management alternatives according to the multiple objectives formulated by the different sectors/participants. This allows more informed and transparent decision-making processes for the Andarax river basin, recognizing both the socio-economic and environmental dimensions of water resources management.  相似文献   

Geochronological problems related to polymetamorphism in the Limpopo Complex, South Africa     

D.D. Van Reenen  R. Boshoff  C.A. Smit  L.L. Perchuk  J.D. Kramers  S. McCourt  R.A. Armstrong 《Gondwana Research》2008,14(4):644

The integration of new and published geochronologic data with structural, magmatic/anatectic and pressure–temperature (P–T) process information allow the recognition of high-grade polymetamorphic granulites and associated high-grade shear zones in the Central Zone (CZ) of the Limpopo high-grade terrain in South Africa. Together, these two important features reflect a major high-grade D₃/M₃ event at ~ 2.02 Ga that overprinted the > 2.63 Ga high-grade Neoarchaean D₂/M₂ event, characterized by SW-plunging sheath folds. These major D₂/M₂ folds developed before ~ 2.63 Ga based on U–Pb zircon age data for precursors to leucocratic anatectic gneisses that cut the high-grade gneissic fabric. The D₃/M₃ shear event is accurately dated by U–Pb monazite (2017.1 ± 2.8 Ma) and PbSL garnet (2023 ± 11 Ma) age data obtained from syntectonic anatectic material, and from sheared metapelitic gneisses that were completely reworked during the high-grade shear event. The shear event was preceded by isobaric heating (P = ~ 6 kbar and T = ~ 670–780 °C), which resulted in the widespread formation of polymetamorphic granulites. Many efforts to date high-grade gneisses from the CZ using PbSL garnet dating resulted in a large spread of ages (~ 2.0–2.6 Ga) that reflect the polymetamorphic nature of these complexly deformed high-grade rocks.  相似文献   

Groundwater flow in the vicinity of two artificial recharge ponds in the Belgian coastal dunes     

A. Vandenbohede  Emmanuel Van Houtte  Luc Lebbe 《Hydrogeology Journal》2008,16(8):1669-1681

Since July 2002, tertiary treated wastewater has been artificially recharged through two infiltration ponds in the dunes of the Belgian western coastal plain. This has formed a lens of artificially recharged water in the dunes’ fresh water lens. Recharged water is recovered by extraction wells located around the ponds. Hydraulic aspects of the artificial recharge and extraction are described using field observations such as geophysical borehole loggings and a tracer test. Borehole logs indicate recharged water up to 20 m below surface, whereas the tracer test gives field data about the residence times of the recharged water. Furthermore, a detailed solute transport model was made of the area surrounding the ponds. Groundwater flow, capture zone, residence times and volume of recharged water in the aquifer are calculated. This shows that the residence time varies between 30 days and 5 years due to the complex flow pattern. The extracted water is a mix of waters with different residence times and natural groundwater, assuring a relatively stable water quality of the extracted water.  相似文献   

Climate response of rainfed versus irrigated farms: the bias of farm heterogeneity in irrigation     

Janka Vanschoenwinkel  Steven Van Passel 《Climatic change》2018,147(1-2):225-234

Researchers who do not take into account farm heterogeneity in implementing specific climate change adaptation options might significantly bias their findings. To prove this point, this paper focusses on irrigation as an adaptation option to climate change and highlights the fact that there is no such thing as “irrigation.” Instead, different farms consider water management options across a spectrum that ranges from purely rainfed farms to purely irrigated farms with in between the extreme practices such as supplemental irrigation, water conservation practices, and different irrigation techniques. Accounting for such differences is necessary, yet difficult due to a lack of farm-specific data on water management and irrigation. This paper uses unique Farm Accountancy Data Network data of Western European farmers on the proportion of farmland that each farm irrigates. Unlike previous work, this allows taking into account some within-irrigation heterogeneity instead of simply categorizing farms as being “irrigated.” We estimate and compare climate response models based on the Ricardian cross-sectional method for a large range of irrigation categories. The results give insights into how the farm irrigation climate response can be significantly different depending on how irrigation is defined. This proves that ignoring within-adaptation differences when comparing non-adaptation with adaptation (in this case, rainfed versus irrigated agriculture) might lead to biased conclusions with regard to effectiveness of adaptation strategies. We therefore argue that it might be more relevant to understand at which point and under which circumstances irrigated agriculture is more or less beneficial than rainfed agriculture.  相似文献   

The cost of achieving South Africa’s ‘fair share’ of global climate change mitigation     

Hugo Van Zyl  Yvonne Lewis  James Kinghorn  James Reeler 《Climate Policy》2018,18(10):1327-1339

Global climate change mitigation action is hampered by systematic under-assessment of national ‘fair shares’, largely on the basis of perceived national interests. This paper aims to inform discussions centred on South Africa’s nationally determined contribution (NDC) by estimating (1) emissions reduction pathways for the country using the Climate Equity Reference Calculator (CERC) assuming a maximum 2°C aggregate warming target and (2) the likely economy-wide net mitigation costs or savings associated with reaching these pathways if known lower-cost mitigation measures, identified through the national mitigation potential analysis, are prioritised. The cumulative net savings associated with achieving the CERC ‘fair share’ emissions pathway, assuming the moderate use of low carbon power generation measures, would reach $5.3 billion by 2030. Net savings could be substantially greater reaching $46.8 billion by 2030 assuming power generation focuses on moving towards full decarbonisation. An unconditional commitment to the mitigation action implied by the ‘fair share’ emissions pathway therefore seems reasonable and prudent purely from the point of view of net country-wide savings. Only if power generation moves towards full decarbonisation would there be a reasonable chance of achieving the more ambitious CERC domestic emissions pathway. However, the significant additional cost associated with achieving the domestic emissions pathway should be conditional on international assistance.

Key policy insights

• South Africa can only achieve its ‘fair share’ of the global mitigation effort if greater use is made of renewable energy options, and can realise significant net savings if it does so.

• Further emissions reductions would incur costs and require significant upscaling of the share of renewable energy and full implementation of all non-power generation mitigation measures available.

• Committing to this further mitigation action contingent on international finance would both strengthen the nation’s position in climate negotiations and support the provision of finance for those vulnerable developing nations that bear little or no responsibility for climate change.

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Positional drift within groups of Type I solar radio bursts     

J. Van Nieuwkoop 《Solar physics》1986,103(1):129-140

In the dynamic spectrograms of the 60-channel solar radiospectrograph at Dwingeloo coherent groups of Type I bursts have been selected. At 243 MHz the positions of the bursts were measured. Within many groups the bursts showed a systematic angular displacement with time. Movements with apparent velocities up to 15000 km s^–1 have been observed. The burst positions have been obtained with a two-element interferometer. A special data reduction method used the amplitude variation of the Type I bursts as a parameter for selection against the background radiation.  相似文献