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31.
32.
Jan?Pa?avaEmail author Ivan?Vav?ín Ji?í?Fryda Vojtěch?Janou?ek Emil?Jelínek 《Mineralium Deposita》2003,38(3):298-311
The Ransko gabbro-peridotite massif in Eastern Bohemia is a strongly differentiated intrusive complex of Lower Cambrian age. The complex hosts low grade Ni-Cu ores mainly developed close to the contact of olivine-rich rocks with gabbros, in troctolites and, to a much lesser extent, in both pyroxene and olivine gabbros and plagioclase-rich peridotites. The ore zone is characterized by strong serpentinization and uralitization. The total Ni + Cu locally reaches up to 4 wt%. Anomalous concentrations of platinum-group elements (PGE's) (maximum 532 ppb Pd, 182 ppb Pt, 53 ppb Rh, 15 ppb Ru, 41 ppb Ir) were detected in samples of Cu-Ni and Ni-Cu ores (maximum 2.63 wt% Ni and 2.31 wt% Cu) from the Jezírka orebody. The main ore paragenesis includes pyrrhotite, pentlandite, chalcopyrite, cubanite, pyrite, magnetite, mackinawite, valleriite, ilmenite and sphalerite. During this work, michenerite, froodite, sperrylite, gold, native bismuth, altaite, tsumoite, hessite, an unnamed Bi-Ni telluride, cobaltite-gersdorffite and galena were newly identified. The host rocks originated through partial melting of a slightly depleted mantle source with noble metals scavenged from this primitive magma prior to the development of these rocks. 相似文献
33.
Min?Luo Cong-Sheng?ZengEmail author Chuan?Tong Jia-Fang?Huang Kai?Chen Feng-Qin?Liu 《Estuaries and Coasts》2016,39(6):1679-1693
Incubation experiments were adopted to characterize the rates and pathways of iron reduction and the contributions to anaerobic organic matter mineralization in the upper 0–5 cm of sediments along a landscape-scale inundation gradient in tidal marsh sediments in the Min River Estuary, Southeast China. Similar sediment characteristics, single-species vegetation, varied biomass and bioturbation, distinct porewater pH, redox potential, and electrical conductivity values have resulted in a unique ecogeochemical zonation along the inundation gradient. Decreases in solid-phase Fe(III) and increases in nonsulfidic Fe(II) and iron sulfide were observed in a seaward direction. Porewater Fe2+ was only detected in the upland area. High rates of iron reduction were observed in incubation jars, with significant accumulations of nonsulfidic Fe(II), moderate accumulations of iron sulfides, and negligible accumulations of porewater Fe2+. Most of the iron reduction was microbially mediated rather than coupled to reduced sulfides. Microbial iron reduction accounted for 20–89 % of the anaerobic organic matter mineralization along the inundation gradient. The rate and dominance of microbial iron reduction generally decreased in a seaward direction. The contributions of microbial iron reduction to anaerobic organic matter mineralization depended on the concentrations of bioavailable Fe(III), the spatial distribution of which was significantly related to tidal inundation. Our results clearly showed that microbial iron reduction in the upper sediments along the gradient is highly dependent on spatial scales controlled primarily by tidal inundation. 相似文献
34.
Mapping Disastrous Natural Hazards Using Global Datasets 总被引:3,自引:0,他引:3
The increased interest for categorising countries at risk calls for an improved methodology allowing comparison of natural hazard impacts at a global level. A disaster is the intersection between a hazardous event, the elements at risk (population, infrastructures) and their vulnerability. In order to associate reported impacts with affected elements and socio-economic or geophysical contextual parameters, geographical location and extent of hazards is needed. The scope of this paper is to present improved automated procedures for a rapid mapping of large disastrous hazard events (floods, earthquakes, cyclones and volcanoes) using Geographical Information Systems (GIS) and available global datasets. Up to 82% of the events and 88% of the reported victims could be geo-referenced and the results highlight both the potentialities and limitations of the methods applied. 相似文献
35.
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Fernando?Henrique?Bucco?TallaricoEmail author Neal?Jesse?McNaughton David?Ian?Groves Ian?R.?Fletcher Bernardino?Ribeiro?Figueiredo Jéssica?Beatriz?Carvalho José?Luzimar?Rego Alfredo?Rossetto?Nunes 《Mineralium Deposita》2004,39(1):68-86
The Breves deposit in the Carajás Copper-Gold Belt, Brazil, a member of the Cu-Au-(W-Bi-Sn) group of deposits, contains about 50 Mt of 1.22% Cu, 0.75 g/t Au, 2.4 g/t Ag, 1,200 g/t W, 70 g/t Sn, 175 g/t Mo and 75 g/t Bi. It is hosted by sandstones and siltstones of the Águas Claras Formation (minimum age of 2,681±5 Ma) in the roof zone of a complex, highly altered granite intrusion. The mineralisation is disseminated in a greisenized zone, resulting from alteration of probable monzogranites and syenogranites. The ore-bearing greisen contains abundant xenomorphic quartz in association with Fe-chlorite and muscovite. The gangue assemblage also includes fluorite, tourmaline, and minor amounts of monazite, xenotime, chlorapatite, thorite, zircon, calcite, siderite and bastnäesite. Copper mineralisation is dominated by chalcopyrite associated with pyrite, arsenopyrite, pyrrhotite and molybdenite. Gold particles, in equilibrium with native bismuth, are common as inclusions in chalcopyrite. The greisen contains sub-economic concentrations of tungsten and niobium that are related to the presence of ferberite, qitianlingite and Nb-rutile. SHRIMP II zircon dating of the host granites gives 207Pb/206Pb ages of 1,878±8 and 1,880±9 Ma for two phases, and a combined age of 1,879±6 Ma. SHRIMP II dating of monazite and xenotime grains in late- to post-mineralisation veins gives a combined 207Pb/206Pb age of 1,872±7 Ma, indistinguishable from the ages of the granites. This provides a genetic connection between the Breves deposit and the ca. 1.88 Ga A-type granite magmatism that typifies the Carajás Belt as part of a much larger, intracratonic magmatic province that extends over much of the Amazonian Craton. The recognition of this association has exploration implications, not only for the geophysical signature of the granite roof zones, but also for likely geochemical dispersion around the deposits of this type.Editorial handling: G. Beaudoin 相似文献
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38.
WEN Lingjuan LU Huayu & QIANG Xiaoke State Key Laboratory of Loess Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an China 《中国科学D辑(英文版)》2005,48(9):1452-1462
In recent years, the Red Clay deposits underlying Quaternary loess on the Chinese Loess Plateau (north China) have attracted more attention because they show a direct and continuous record of past atmos- pheric circulation and palaeoclimatic change. Investiga- tions on Red Clay deposits through multidisciplinary methods have demonstrated an aeolian origin for the Red Clay, like the overlying Quaternary loess. The Red Clay formed during the Miocene and Pliocene[1―13]. However, the type o… 相似文献
39.
Wan Zheng 《地震工程与工程振动(英文版)》2015,14(2):229-238
A simple cyclic elastoplastic constitutive model for sand is proposed based on the UH model for overconsolidated clay. The proposed model has the following features. First, in order to describe the stress-induced anisotropy in sand, a rotational hardening rule is introduced for the evolution of the yield surface axis with development of plastic deviatoric strain in the principal stress space. Second, the relationship between the rotational axis and stress-induced anisotropy is modeled by introducing the slope of rotational axis into the yield function. The fl atness of the yield surface can be determined by the slope of rotational axis. Finally, a revised unifi ed hardening parameter is proposed to incorporate the stress-induced anisotropy. The model capability in describing the cyclic response of sand is verifi ed by comparing the simulations with available test results. 相似文献
40.
Chris Soulsby Bernhard Scheliga Aaron Neill Jean-Christophe Comte Doerthe Tetzlaff 《水文研究》2021,35(6):e14206
The drought of summer 2018, which affected much of Northern Europe, resulted in low river flows, biodiversity loss and threats to water supplies. In some regions, like the Scottish Highlands, the summer drought followed two consecutive, anomalously dry, winter periods. Here, we examine how the drought, and its antecedent conditions, affected soil moisture, groundwater storage, and low flows in the Bruntland Burn; a sub-catchment of the Girnock Burn long-term observatory in the Scottish Cairngorm Mountains. Fifty years of rainfall-runoff observations and long-term modelling studies in the Girnock provided unique contextualisation of this extreme event in relation to more usual summer storage dynamics. Whilst summer precipitation in 2018 was only 63% of the long-term mean, soil moisture storage across much of the catchment were less than half of their summer average and seasonal groundwater levels were 0.5 m lower than normal. Hydrometric and isotopic observations showed that ~100 mm of river flows during the summer (May-Sept) were sustained almost entirely by groundwater drainage, representing ~30% of evapotranspiration that occurred over the same period. A key reason that the summer drought was so severe was because the preceding two winters were also dry and failed to adequately replenish catchment soil moisture and groundwater stores. As a result, the drought had the biggest catchment storage deficits for over a decade, and likely since 1975–1976. Despite this, recovery was rapid in autumn/winter 2018, with soil and groundwater stores returning to normal winter values, along with stream flows. The study emphasizes how long-term data from experimental sites are key to understanding the non-linear flux-storage interactions in catchments and the “memory effects” that govern the evolution of, and recovery from, droughts. This is invaluable both in terms of (a) giving insights into hydrological behaviours that will become more common water resource management problems in the future under climate change and (b) providing extreme data to challenge hydrological models. 相似文献