Hydrofluoric Acid‐Free Digestion of Geological Samples for the Quantification of Rare Earth Elements by Inductively Coupled Plasma‐Optical Emission Spectrometry     

Andrey Linhares Bezerra de Oliveira  Júlio Carlos Afonso  Lilian da Silva  Arnaldo Alcover Neto  Manuel Castro Carneiro  Lílian Irene Dias da Silva  Maria Inês Couto Monteiro 《Geostandards and Geoanalytical Research》2019,43(4):689-699

Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H₃PO₄ is safer than HF, NH₄F or NH₄HF₂ aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method.  相似文献   

Magnetic Basement Depth Inversion in the Space Domain     

Tiago Mane Nunes  Valéria Cristina F. Barbosa  João Batista C. Silva 《Pure and Applied Geophysics》2008,165(9-10):1891-1911

We present a total-field anomaly inversion method to determine both the basement relief and the magnetization direction (inclination and declination) of a 2D sedimentary basin presuming negligible sediment magnetization. Our method assumes that the magnetic intensity contrast is constant and known. We use a nonspectral approach based on approximating the vertical cross section of the sedimentary basin by a polygon, whose uppermost vertices are forced to coincide with the basin outcrop, which are presumably known. For fixed values of the x coordinates our method estimates the z coordinates of the unknown polygon vertices. To obtain the magnetization direction we assume that besides the total-field anomaly, information about the basement’s outcrops at the basin borders and the basement depths at a few points is available. To obtain stable depth-to-basement estimates we impose overall smoothness and positivity constraints on the parameter estimates. Tests on synthetic data showed that the simultaneous estimation of the irregular basement relief and the magnetization direction yields good estimates for the relief despite the mild instability in the magnetization direction. The inversion of aeromagnetic data from the onshore Almada Basin, Brazil, revealed a shallow, eastward-dipping basement basin.  相似文献   

Reply to the comments by Mauz, B. and Antonioli, F. on “Sea Level and Climate Changes during OIS 5e in the Western Mediterranean”     

T. Bardají  J.L. Goy  C. Zazo  Cl. Hillaire-Marcel  C.J. Dabrio  A. Cabero  B. Ghaleb  P.G. Silva  J. Lario 《Geomorphology》2009,110(3-4):231-235

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Ground-roll attenuation using a 2D time-derivative filter     

Paulo E. M. Melo  Milton J. Porsani  Michelângelo G. Silva 《Geophysical Prospecting》2009,57(3):343-353

We present a new filtering method for the attenuation of ground-roll. The method is based on the application of a bi-dimensional filter for obtaining the time-derivative of the seismograms. Before convolving the filter with the input data matrix, the normal moveout correction is applied to the seismograms with the purpose of flattening the reflections. The method can locally attenuate the amplitude of data of low frequency (in the ground-roll and stretch normal moveout region) and enhance flat events (reflections). The filtered seismograms can reveal horizontal or sub-horizontal reflections while vertical or sub-vertical events, associated with ground-roll, are attenuated. A regular set of samples around each neighbourhood data sample of the seismogram is used to estimate the time-derivative. A numerical approximation of the derivative is computed by taking the difference between the interpolated values calculated in both the positive and the negative neighbourhood of the desired position. The coefficients of the 2D time-derivative filter are obtained by taking the difference between two filters that interpolate at positive and negative times. Numerical results that use real seismic data show that the proposed method is effective and can reveal reflections masked by the ground-roll. Another benefit of the method is that the stretch mute, normally applied after the normal moveout correction, is unnecessary. The new filtering approach provides results of outstanding quality when compared to results obtained from the conventional FK filtering method.  相似文献   

Modelling and migration with orthogonal isochron rays     

Eduardo Filpo Ferreira da Silva  Paul Sava 《Geophysical Prospecting》2009,57(5):773-784

For increasing time values, isochrons can be regarded as expanding wavefronts and their perpendicular lines as the associated orthogonal isochron rays. The speed of the isochron movement depends on the medium velocity and the source-receiver position. We introduce the term equivalent-velocity to refer to the speed of isochron movement. In the particular case of zero-offset data, the equivalent velocity is half of the medium velocity. We use the concepts of orthogonal isochron-rays and equivalent velocity to extend the application of the exploding reflector model to non-zero offset imaging problems. In particular, we employ these concepts to extend the use of zero-offset wave-equation algorithms for modelling and imaging common-offset sections. In our imaging approach, the common-offset migration is implemented as a trace-by-trace algorithm in three steps: equivalent velocity computation, data conditioning for zero-offset migration and zero-offset wave-equation migration. We apply this methodology for modelling and imaging synthetic common-offset sections using two kinds of algorithms: finite-difference and split-step wavefield extrapolation. We also illustrate the isochron-ray imaging methodology with a field-data example and compare the results with conventional common-offset Kirchhoff migration. This methodology is attractive because it permits depth migration of common-offset sections or just pieces of that by using wave-equation algorithms, it extends the use of robust zero-offset algorithms, it presents favourable features for parallel processing, it permits the creation of hybrid migration algorithms and it is appropriate for migration velocity analysis.  相似文献   

Dynamics of a Prorocentrum minimum bloom along the northern coast of Sinaloa,Mexico     

Aída Martínez-López  Diana Cecilia Escobedo-Urías  Ana Elsi Ulloa-Pérez  Raul Aguirre 《Continental Shelf Research》2008

To investigate the relative importance of mesoscale physical events, such as upwellings and physical and chemical variables during an algae bloom of Prorocentrum minimum, 25 sampling sites were established offshore of the Navachiste Lagoon Complex on the east side of the Gulf of California. Samples were analyzed for phytoplankton concentration, water chemistry, and temperature during November 1999, January, March, April, May, and August 2000. Satellite imagery of sea surface temperature (SST) for April 2000 was processed to obtain a synoptic view of the area during the extraordinary bloom of P. minimum in the open waters of the Gulf of California. The bloom was associated with change of oceanographic conditions from moderate winds to calm period, temperature increase and high nitrate (NO₃⁻-N) and ammonia (NH₄⁺-N) content in the offshore waters. Depletion of these nutrients during the bloom suggests that this species uses both types of nitrogen substrates. Cysts in the northernmost sampling stations in January and March indicate that upwelling water, rich in nitrates, also carried a seed stock population of P. minimum. SST patterns in the satellite imagery suggest wind-forcing as the responsible mechanisms triggering the algal bloom offshore of the Navachiste Lagoon Complex.  相似文献   

Environmental influences on soil CO₂ degassing at Furnas and Fogo volcanoes (São Miguel Island,Azores archipelago)     

F. Viveiros  T. Ferreira  J. Cabral Vieira  C. Silva  J.L. Gaspar 《Journal of Volcanology and Geothermal Research》2008

Since October 2001, four soil CO₂ flux stations were installed in the island of São Miguel (Azores archipelago), at Fogo and Furnas quiescent central volcanoes. These stations perform measurements by the accumulation chamber method and, as the gas flux may be influenced by external variables, the stations are equipped with several meteorological sensors. Multivariate regression analysis applied to the large datasets obtained allowed observing that the meteorological variables may influence the soil CO₂ flux oscillations from 18% to 50.5% at the different monitoring sites. Additionally, it was observed that meteorological variables (mainly soil water content, barometric pressure, wind speed and rainfall) play a different role in the control of the gas flux, depending on the selected monitoring site and may cause significant short-term (spike-like) fluctuations. These divergences may be potentially explained by the porosity and hydraulic conductivity of the soils, topographic effects, drainage area and different exposure of the monitoring sites to the weather conditions. Seasonal effects are responsible for long-term oscillations on the gas flux.  相似文献   

北京及邻区长城纪火山事件的沉积记录   总被引：6，自引：1，他引：5  

和政军  宋天锐 《沉积学报》2000,18(4):510-514,520

北京及邻区的中元古代大红峪组中发育着与火山事件有关的沉积相,主要包括两种基本类型:火山源硅质-陆源砂-碳酸盐岩混积相和火山碎屑重力流沉积,后者又可分为火山碎屑基浪沉积相和火山-沉积角砾碳酸盐岩混积相。初步分析表明,大红峪期大量的硅质沉积主要来自同期的水下火山活动;火山碎屑基浪沉积与火山口内残余热气冲破熔岩封堵而爆发泄出,造成一定范围的海水涌浪作用有关。  相似文献   

Comparison Between Kriging Variance and Interpolation Variance as Uncertainty Measurements in the Capanema Iron Mine, State of Minas Gerais—Brazil     

Marcelo Monteiro da Rocha  Jorge Kazuo Yamamoto 《Natural Resources Research》2000,9(3):223-235

The Capanema Mine, an iron ore deposit, is located in the central portion of the Quadrilátero Ferrífero, State of Minas Gerais, southeastern Brazil. Mine development data from approximately 7000 drillholes were used for a comparative study between kriging variance and interpolation variance as uncertainty measurements associated with ordinary kriging estimates. As known, the traditional kriging variance does not depend on local data and, therefore, does not measure the actual dispersion of data. On the other hand, the interpolation variance measures adequately the local dispersion of data used for an ordinary kriging estimate. This paper presents an application of the concept of interpolation variance for measuring uncertainties associated with ordinary kriging estimates of Fe and silica grades. These data were selected for their distinct statistical characteristics with Fe presenting a negatively skewed distribution and, consequently, a low dispersion, and silica a positively skewed distribution and, therefore, a high variability. Comparative studies between the two uncertainty measurements associated with ordinary kriging estimates of Fe and silica proved the superiority of the interpolation variance as a reliable and precise alternative to the kriging variance.  相似文献   

危险目标再入跟踪预报研究     

吴连大  王昌彬 《紫金山天文台台刊》2000,19(2):100-105

本文讨论了危险目标再入的有关问题,通过２２８７０和２５１００两个卫星陨落期预报的实践,我们形成了一种计算卫星落点的方法,方法的基本要点是：１算准卫星的面质比;２在１８０公里以下,考虑阻尼系数随高度（大气密度）的变化;３在计算落点时,使用两组根数,调整面质比使两组根数计算的落点基本相同,并验证面质比调整的合理性;４对于ＭＳＩＳ－１９９０模式,我们发现调整后的面质比要比理论的面质比大１．０９倍,也许这  相似文献