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931.
A modification of the spectrophotometric method for the determination of fluoride ions in iron‐rich materials is proposed. In this method the iron matrix was successfully removed using Diphonix® resin. The studied sample was a ferruginous mineral which contained about 38% of iron. The Euronorm certified reference material (ECRM) 676‐1 (Iron Ore Sinter), as a commercially available material having a similar matrix (39.76% w/w Fe) and fluoride level (0.1% w/w), was used to validate the method. After partial digestion in concentrated hydrochloric acid the samples were diluted and passed through Diphonix® resin. The concentration of fluoride ions was determined by a spectrophotometric method using a Zr:ER complex (λ = 540 nm). The result obtained for the ECRM was in good agreement with the certificate specification and thus proved the method to be applicable for the determination of fluoride ions in iron‐rich materials. Due to the easy digestion step and simple requirements for equipment, this method can be used in most laboratories. 相似文献
932.
Alicia Kirschbaum Jesica Murray Emilce López Ahinoam Equiza Marcelo Arnosio Geraldo Boaventura 《Environmental Earth Sciences》2012,65(2):493-504
The Yacoraite River and its tributaries run down the eastern slope of the Aguilar Range. It is one of the tributaries of the
Rio Grande, located in Quebrada de Humahuaca, a UNESCO World Heritage site. The Aguilar underground mine (Pb–Ag–Zn) is located
in the upper reaches of the Yacoraite River drainage basin. The aim of this work is to characterize the presence of heavy
metals in water and sediments of the Yacoraite River and to identify their sources. The analysis shows the seasonal variation
of heavy metals concentration in water and their relation with the World Health Organization (WHO) limits established for
human consumption. The Yacoraite basin is naturally anomalous in some metals and some elements, such as As which is controlled
by the chemical composition of regional lithology. During the wet season, Al, Co, Mo and Pb concentrations in water samples
are higher than during the dry season; in addition, these metals are also higher than WHO limit values. High enrichment factors
for Ba, Mo, Pb, Zn and Cd were found in Casa Grande stream, indicating the direct influence of the mining activities. Cd,
Pb and Zn are present in the Aguilar ore minerals, such as sphalerite and galena. Sediments collected during the dry season
show a drastic increase in the concentration of As, Pb, Ba, Zn, Cd and Mn. The Müller geo-accumulation index in Casa Grande
indicates that it is a highly polluted stream. The concentrations of As, Pb, Ba, Zn, Cd are also high in Yacoraite River: Security Quality Guidelines indicates
toxicity. A decrease in enrichment factors and geo-accumulation indices observed in sediments indicates the occurrence of precipitation/adsorption
processes in the river to restore the equilibrium composition. Strict environmental controls in Aguilar Mine are necessary
to avoid the uncontrolled input of toxic metals in Casa Grande stream and Yacoraite River. 相似文献
933.
Pilar García-Soidán Raquel Menezes Óscar Rubiños-López 《Environmental Earth Sciences》2012,66(2):615-624
The use of kriging for construction of prediction or risk maps requires estimating the dependence structure of the random
process, which can be addressed through the approximation of the covariance function. The nonparametric estimators used for
the latter aim are not necessarily valid to solve the kriging system, since the positive-definiteness condition of the covariance
estimator typically fails. The usage of a parametric covariance instead may be attractive at first because of its simplicity,
although it may be affected by misspecification. An alternative is suggested in this paper to obtain a valid covariance from
a nonparametric estimator through the Fourier series tool, which involves two issues: estimation of the Fourier coefficients
and selection of the truncation point to determine the number of terms in the Fourier expansion. Numerical studies for simulated
data have been conducted to illustrate the performance of this approach. In addition, an application to a real environmental
data set is included, related to the presence of nitrate in groundwater in Beja District (Portugal), so that pollution maps
of the region are generated by solving the kriging equations with the use of the Fourier series estimates of the covariance. 相似文献
934.
María del Carmen Blanco Juan Darío Paoloni Hector Morrás Carmen Fiorentino Mario Eduardo Sequeira Nilda N. Amiotti Oscar Bravo Silvana Diaz Martín Espósito 《Environmental Earth Sciences》2012,66(7):2075-2084
Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L−1) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations
(loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters
are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated
aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in
waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L−1; in 27% As concentrations ranged from 10 to 50 μg L−1 and in 58% it reached 60–500 μg L−1. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba
(p < 0.01; r
2 = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r
2 = 0.85) and As–Cr (p < 0.05; r
2 = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption
processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding
the guideline value for drinking water. 相似文献
935.
936.
937.
Lóránt Bíró Márta Polgári Tivadar M. Tóth Tamás Vigh 《Central European Journal of Geosciences》2012,4(3):478-494
Although the úrkút manganese ore deposit in western placecountry-regionHungary has been exploited for at least 90 years, there are still numerous open questions concerning ore genetics as well as structure and geometry of the ore body. A large set of available archive data for the deposit have been reviewed and evaluated in order to solve some of the most crucial problems. For processing, besides diverse GIS approaches, univariate and multivariate statistical methods were used on the created unified database. The main aims of the mathematical treatment were giving a classification scheme for the wide spectrum of Mn-ores based on their chemical composition (Mn, Fe, Si, P) as well as evaluation of their spatial distribution. For the ore characterization and understanding the genetic processes, cluster and discriminant function analyses were used. Results of the multivariate treatment verified the existence of different ore types and provided an exact chemical definition for all of them. It alsoinferred that the main geochemical processes that took place in ore genesis were similar for all sample groups (ore types) with significantly different weights in each case. A 3D evaluation of the úrkút mine heading map system shows that the ore body covers the footwall surface as a stratiform sheet throughout the study area. Palaeo-relief studies suggest a significant difference between the footwall and hanging wall morphologies which clearly implies tectonic activity following ore deposition. The deposit was affected by an E-W compression stress field near the Aptian-Albian transition causing folding of the Mn deposit. 相似文献
938.
Pattern and timing of the northwestern Barents Sea Ice Sheet deglaciation and indications of episodic Holocene deposition 总被引:1,自引:0,他引:1
Denise Christina Rüther Lilja Rún Bjarnadóttir Juho Junttila Katrine Husum Tine Lander Rasmussen Renata Giulia Lucchi Karin Andreassen 《Boreas: An International Journal of Quaternary Research》2012,41(3):494-512
The origin of two acoustic sediment units has been studied based on lithological facies, chronology and benthic stable isotope values as well as on foraminifera and clay mineral assemblages in six marine sediment cores from Kveithola, a small trough west of Spitsbergenbanken on the western Barents Sea margin. We have identified four time slices with characteristic sedimentary environments. Before c. 14.2 cal. ka, rhythmically laminated muds indicate extensive sea ice cover in the area. From c. 13.9 to 14.2 cal. ka, muds rich in ice‐rafted debris were deposited during the disintegration of grounded ice on Spitsbergenbanken. From c. 10.3 to 13.1 cal. ka, sediments with heterogeneous lithologies suggest a shifting influence of suspension settling and iceberg rafting, probably derived from a decaying Barents Sea Ice Sheet in the inner‐fjord and land areas to the north of Kveithola. Holocene deposition was episodic and characterized by the deposition of calcareous sands and shell debris, indicative of strong bottom currents. We speculate that a marked erosional boundary at c. 8.2 cal. ka may have been caused by the Storegga tsunami. Whilst deposition was sparse during the Holocene, Kveithola acted as a sediment trap during the preceding deglaciation. Investigation of the deglacial sediments provides unprecedented details on the dynamics and timing of glacial retreat from Spitsbergenbanken. 相似文献
939.
Evidence for mid- to late-Holocene palaeotsunami deposits,Kakawis Lake,Vancouver Island,British Columbia 总被引:1,自引:1,他引:0
Gloria I. López 《Natural Hazards》2012,60(1):43-68
Kakawis Lake situated four metres above sea level on western Vancouver Island, British Columbia, Canada, was the target of
a palaeotsunami investigation. Six percussion cores recovered from this lake contain six anomalous deposits interbedded within
the unconsolidated lacustrine sediments. Detailed sedimentological, geophysical and macro-fraction analyses were performed.
The methods new to palaeoseismic approaches proved to be successful tools to characterize the anomalously coarse layers enriched
in terrestrial plant detritus and marine shells. Based on at least eight types of evidence, six tsunami inundations are suggested
as mechanisms responsible for the anomalous deposition, spanning from 3,634 to 2,534 cal yrs BP. Each tsunami event consists
of a combination of different lithological facies resulting from different stages of tsunami inundation and settling of the
material in the lake basin (pulses and inter-pulses). Tsunami deposits in lakes are shown to be less vulnerable to erosional
and bioturbation processes than those found in marshes or beaches as well as underwater marine environments. However, few
palaeoseismic studies have been carried out in low-elevation lakes along the Cascadia Subduction Zone region. The three last
tsunami events known to have inundated areas along the Pacific shores of southern British Columbia, Canada and northern USA
are not present at Kakawis Lake, establishing a current <4 m above mean sea level vertical limit as possible maximum tsunami
height for areas located away from fjord heads on Vancouver Island. The anomalous deposits found in Kakawis Lake may be the
oldest geological evidence of inferred tsunami on Vancouver Island, providing a possible recurrence interval between 200 and
400 years. 相似文献
940.
Kyounghee Yang Csaba Szabó Shoji Arai Jae-Eun Yu Hoonyeong Jung 《Mineralogy and Petrology》2012,106(1-2):107-130
Group II xenoliths, corresponding to the lithology of dunite, wehrlite to olivine clinopyroxenite and olivine websterite to websterite, occur in Pleisto-Holocene alkali basalts from Jeju Island, South Korea. The large grain size (up to 5?mm), moderate mg# [=100?×?Mg/(Mg?+?Fetotal) atomic ratio] of olivine (79–82) and pyroxenes (77–83), and absence of metamorphic textural features indicate that they are cumulates of igneous origin. Based on textural features, mineral equilibria and major and trace element variations, it can be inferred that the studied xenoliths were crystallized from basaltic melts enriched in incompatible trace elements and belong to the Jeju Pleisto-Holocene magma system. They appear to have been emplaced near the present Moho, an estimated 5–8?kbars beneath Jeju Island. Consolidation of cumulates was followed by infiltration of silica-enriched metasomatic melt, producing secondary orthopyroxenes at the expense of olivine. The metasomatic agent appears to have been a silica-enriched residual melt evolved from an initially slightly silica-undersaturated alkali basalt to silica-saturated compositions by fractional crystallization under relatively high pressure conditions. The result of this study indicates that relatively young olivine-bearing cumulates could have been metasomatized by a silica-enriched melt within underplates, suggesting that silica enrichment can occur in intraplate Moho-related rocks as well as in the upper mantle of the subarc area. 相似文献