Exploration for Mississippi-Valley type stratabound Zn ores with stream suspensates and stream sediments, Virginia, U.S.A.     

Frederic R. Siegel 《Journal of Geochemical Exploration》1990,38(3)

Suspended and equivalent active sediments were collected from streams at 84 sites at the eastern and western sides of a ridge with stratabound Zn mineralization, Rockingham County, Virginia (USA). The purpose was to evaluate the relative effectiveness of suspended and bottom sediment in the geochemical exploration for Mississippi-Valley type Zn ores. The orebody is composed of sphalerite and minor amounts of galena with some chalcopyrite, strikes parallel to the enclosing dolomite beds at N34°E, and cuts vertically across the 30°SE dip. Oxidation of the ore extends to about 100 m in depth.Zinc was effective in detecting the mineralized zone. Zinc in the suspensates provided a denser anomaly system (7 strong and 2 moderate samples) than Zn in the <150 μm size of the bottom sediment, either totally dissolved (4 strong and 1 moderate anomalies) or extracted with cold 3% HCl (5 strong and 3 moderate anomalies). The magnitude of the high values for suspensate Zn was considerably higher than those for the other sample types studied. Suspensate Zn was complemented by 3 strong suspensate Cu anomalies. The suspensate Zn anomaly dispersion was about 850 m, 400 m of which was upstream from the mineralization. Lead was detected only in the cold acid extraction and in combination with Cu and Zn gave an extensive overlapping multielement anomaly string that targeted the ore zone and had a dispersion downstream from the mineralization of more than 1000 m. The Pb anomalies extended about 900 m upstream and 400 m downstream from the ore zone. Together with suspensate Zn, the Pb anomalies suggest a continuation of mineralization upstrike from the known orebody.The major anomaly systems are along the eastern side of the ridge with comparatively few anomalies present in the drainage along the western side. The concentration of anomalies in the eastern drainage and anomaly disposition with respect to known mineralization result from structural control on the hydromorphic dispersion of metals from the orebody.  相似文献   

Increased concentrations of potassium in heartwood of trees in response to groundwater contamination     

Don A. Vroblesky  Thomas M. Yanosky  Frederic R. Siegel 《Environmental Geology》1992,19(2):71-74

The wood of tuliptrees (Liriodendron tulipifera L.) growing above groundwater contamination from a hazardous-waste landfill in Maryland contained elevated concentrations of potassium (K). The groundwater contamination also contained elevated concentrations of dissolved K, as well as arsenic (As), cadmium (Cd), chloride (Cl), iron (Fe), manganese (Mn), zinc (Zn), and organic solvents. The dissolved K is derived from disposed smoke munitions. The excess K in the tuliptrees is concentrated in the heartwood, the part of the xylem most depleted in K in trees growing outside of the contamination. These data show that the uptake and translocation of K by tuliptrees can be strongly influenced by the availability of K in groundwater contamination and suggest the utility of this species as an areal indicator of groundwater contamination.  相似文献   

Representation du potential terrestre par des developpements harmoniques excentres     

Henri Marcel Dufour 《Studia Geophysica et Geodaetica》1970,14(2):109-110

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Liquid water uptake in unconfined Callovo Oxfordian clay-rock studied with neutron and X-ray imaging     

Stavropoulou  Eleni  Andò  Edward  Tengattini  Alessandro  Briffaut  Matthieu  Dufour  Frédéric  Atkins  Duncan  Armand  Gilles 《Acta Geotechnica》2019,14(1):19-33

The Callovo Oxfordian clay-rock (COx) is studied in France for the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity. This paper presents an experimental study into the mechanisms of water uptake in small, unconfined, prismatic specimens of COx, motivated by the comprehension of cracking observed during concrete/COx interface sample preparation. Water uptake is monitored using both X-ray tomography and neutron radiography, the combination of these imaging techniques allowing material deformation and water arrival to be quantified, respectively. Given the speed of water entry and crack propagation, relatively fast imaging is required: 5-min X-ray tomographies and 10-s neutron radiographs are used. In this study, pairs of similar COx samples from the same core are tested separately with each imaging technique. Two different orientations with respect to the core are also investigated. Analysis of the resulting images yields with micro- and macro-scale insights into hydromechanical mechanisms to be obtained. This allows the cracking to be interpreted as a rapid breakdown in capillary suction (supposed large both to drying and rebound from in situ stress state) due to water arrival, which in turn causes a loss of effective stress, allowing cracks to propagate and deliver water further into the material.

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Identifying geochemical reactions on wellbore cement/caprock interface under sequestration conditions     

Małgorzata Labus  Frederic Wertz 《Environmental Earth Sciences》2017,76(12):443

The integrity of wells, which are key components for CO₂ sequestration, depends mainly on the seal between the wellbore cement and the geologic formation. To identify the reaction products that may alter the cement/caprock interface, batch experiments and computer modelling were conducted and analysed. Over time, the dissolution and precipitation of minerals alters the physical properties of the interface, including its tightness. One main objective of the simulation was thus to analyse the evolution of the porosity of cement and caprock over time. The alteration of the cement/caprock interface was identified as a complex problem and differentiated depending on rock type. The characteristic feature of a cement/shale contact zone is the occurrence of a highly carbonated, compacted layer within the shale, which in turn causes cement/shale detachment. In the case of a cement/anhydrite interface, the most important reaction is severe anhydrite dissolution. Secondary calcite precipitation takes place in deeper parts of the rock. The cement/rock contact zone is prone to rapid mineral dissolution, which contributes to increased porosity and may alter the well integrity. Comparison of computer simulations with autoclave experiments enabled the adjustment of unknown parameters. This enhances the knowledge of these particular assemblages. Overall, a good match was obtained between experiments and simulations, which enhances confidence in using models to predict longer-term evolution.  相似文献   

Erratum to “26Al–26Mg and 207Pb–206Pb systematics of Allende CAIs: Canonical solar initial 26Al/27Al ratio reinstated” [Earth Planet Sci. Lett. 272 (2008) 353–364]     

Benjamin Jacobsen  Qing-Zhu Yin  Frederic Moynier  Yuri Amelin  Alexander N. Krot  Kazuhide Nagashima  Ian D. Hutcheon  Herbert Palme 《Earth and Planetary Science Letters》2009,277(3-4):549

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Isotopic fractionation of zinc in tektites     

Frederic Moynier  Pierre Beck  Fred Jourdan  Qing-Zhu Yin  Uwe Reimold  Christian Koeberl 《Earth and Planetary Science Letters》2009,277(3-4):482-489

Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation.For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ^66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ^66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ^66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ^66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ^66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ^66/64Zn = 0–0.7‰ for a diverse spectrum of upper continental crust materials.The elemental abundance of Zn is negatively correlated with δ^66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime.  相似文献   

The influence of sediment size,relative grain size and channel slope on initiation of sediment motion in boulder bed rivers. A lichenometric study     

Frederic Gob  Jean‐Paul Bravard  François Petit 《地球表面变化过程与地形》2010,35(13):1535-1547

Sediment transport of four boulder bed rivers is studied using lichenometry. The presence of lichens on boulders in the river channel is used to date the last mobilization of the blocks. Using size frequency diagrams and regional growth curves calibrated with dated reference points it is possible to determine the flood event responsible for the last mobilization of each boulder with lichens present. The specific stream power of flood events over the last 60 years is then calculated, and thresholds of sediment transport based on the sediment size are calculated. The results from the four studied rivers are compared to similar relationships in the literature. Sediment motion thresholds appear to be very variable within the same type of river (mountainous boulder bed rivers). The critical specific stream power necessary to mobilize a particle of a given diameter may vary by up to 10 times from one river to the next. Bed sediment size and river slope may explain this large range of stream powers. Calculation of the relative size of the transported particles (D_i/D₅₀) also shows that both hiding and protrusion effects, as well as channels slope, are important factors in sediment transport. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Visible–near infrared spectral indices for mapping mineralogy and chemistry with OSIRIS‐REx     

Hannah H. Kaplan  Victoria E. Hamilton  Ellen S. Howell  F. Scott Anderson  M. Antonella Barrucci  John Brucato  Thomas H. Burbine  Beth E. Clark  Ed A. Cloutis  Harold C. Connolly  Elisabetta Dotto  Joshua P. Emery  Sonia Fornasier  Cateline Lantz  Lucy F. Lim  Frederic Merlin  Alice Praet  Dennis C. Reuter  Scott A. Sandford  Amy A. Simon  Driss Takir  Dante S. Lauretta 《Meteoritics & planetary science》2020,55(4):744-765

The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS‐REx) mission is to return to Earth a pristine sample of carbonaceous material from the primitive asteroid (101955) Bennu. To support compositional mapping of Bennu as part of sample site selection and characterization, we tested 95 spectral indices on visible to near infrared laboratory reflectance data from minerals and carbonaceous meteorites. Our aim was to determine which indices reliably identify spectral features of interest. Most spectral indices had high positive detection rates when applied to spectra of pure, single‐component materials. The meteorite spectra have fewer and weaker absorption features and, as a result, fewer detections with the spectral indices. Indices targeting absorptions at 0.7 and 2.7–3 μm, which are attributable to hydrated minerals, were most successful for the meteorites. Based on these results, we identified a set of 17 indices that are most likely to be useful at Bennu. These indices detect olivines, pyroxenes, carbonates, water/OH‐bearing minerals, serpentines, ferric minerals, and organics. Particle size and albedo are known to affect band depth but had a negligible impact on interpretive success with spectral indices. Preliminary analysis of the disk‐integrated Bennu spectrum with these indices is consistent with expectations given the observed absorption near 3 μm. Our study prioritizes spectral indices to be used for OSIRIS‐REx spectral analysis and mapping and informs the reliability of all index‐derived data products, including a science value map for sample site selection.  相似文献   

Global zoogeography of fragile macrozooplankton in the upper 100-1000 m inferred from the underwater video profiler     

Stemmann  Lars; Youngbluth  Marsh; Robert  Kevin; Hosia  Aino; Picheral  Marc; Paterson  Harriet; Ibanez  Frederic; Guidi  Lionel; Lombard  Fabien; Gorsky  Gabriel 《ICES Journal of Marine Science》2008,65(3):433-442

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