Characterization of the binding sites for Al(III) and Be(II) in a sample of marine fulvic acids     

Joaquim C. G. Esteves da Silva  Adlio A. S. C. Machado 《Marine Chemistry》1996,54(3-4)

A sample of coastal marine fulvic acids (mfua) was studied and its binding site structures that form stable complexes with metal ions were identified. A previously developed self-modeling methodology, based on the coupling of synchronous fluorescence (SyF) spectroscopy with evolving factor analysis (EFA), was used for the analysis of the interactions between mfua and two metal ions that act as probes for binding sites, namely Be(II) and Al(III). Two types of binding site structures were detected, probably of the salicylic acid and catechol types. The values of the conditional stability constants between mfua and the two metal ions were: for Be(II), at pH = 6, log K = 5.32(8); for Al(III), at pH = 4, log K = 5.1(2). The concentration of the corresponding binding sites was found to be less than one half of those found for soil fulvic acid samples.  相似文献   

Spatial and temporal zoning of hydrothermal alteration and mineralization in the Sossego iron oxide–copper–gold deposit,Carajás Mineral Province,Brazil: paragenesis and stable isotope constraints     

Lena V. S. Monteiro  Roberto P. Xavier  Emerson R. de Carvalho  Murray W. Hitzman  Craig A. Johnson  Carlos Roberto de Souza Filho  Ignácio Torresi 《Mineralium Deposita》2008,43(2):129-159

The Sossego iron oxide–copper–gold deposit (245 Mt @ 1.1% Cu, 0.28 g/t Au) in the Carajás Mineral Province of Brazil consists of two major groups of orebodies (Pista–Sequeirinho–Baiano and Sossego–Curral) with distinct alteration assemblages that are separated from each other by a major high angle fault. The deposit is located along a regional WNW–ESE-striking shear zone that defines the contact between metavolcano–sedimentary units of the ∼2.76 Ga Itacaiúnas Supergroup and tonalitic to trondhjemitic gneisses and migmatites of the ∼2.8 Ga Xingu Complex. The deposit is hosted by granite, granophyric granite, gabbro, and felsic metavolcanic rocks. The Pista–Sequeirinho–Baiano orebodies have undergone regional sodic (albite–hematite) alteration and later sodic–calcic (actinolite-rich) alteration associated with the formation of massive magnetite–(apatite) bodies. Both these alteration assemblages display ductile to ductile–brittle fabrics. They are cut by spatially restricted zones of potassic (biotite and potassium feldspar) alteration that grades outward to chlorite-rich assemblages. The Sossego–Curral orebodies contain weakly developed early albitic alteration and very poorly developed subsequent calcic–sodic alteration. These orebodies contain well-developed potassic alteration assemblages that were formed during brittle deformation that resulted in the formation of breccia bodies. Breccia matrix commonly displays coarse mineral infill suggestive of growth into open space. Sulfides in both groups of deposits were precipitated first with potassic alteration and more importantly with a later assemblage of calcite–quartz–epidote–chlorite. In the Sequeirinho orebodies, sulfides range from undeformed to deformed; sulfides in the Sossego–Curral orebodies are undeformed. Very late, weakly mineralized hydrolytic alteration is present in the Sossego/Currral orebodies. The sulfide assemblage is dominated by chalcopyrite with subsidiary siegenite, and millerite. Pyrrhotite and pyrite are minor constituents of ore in the Sequerinho orebodies while pyrite is relatively abundant in the Sossego–Curral bodies. Oxygen isotope partitioning between mineral pairs constrains temperatures in the deposit spatially and through time. In the Sequeirinho orebody, the early sodic–calcic alteration stage was characterized by temperatures exceeding 500°C and values for the alteration fluid of 6.9 ± 0.9‰. Temperature declines outward and upward from the zone of most intense alteration. Paragenetically later copper–gold mineralization displays markedly lower temperatures (<300°C) and was characterized by the introduction of ¹⁸O-depleted hydrothermal fluids −1.8 ± 3.4‰. The calculated δD_H2O and values suggest that the fluids that formed the early calcic–sodic alteration assemblage were of formational/metamorphic or magmatic origin. The decrease of values through time may reflect influx of surficially derived waters during later alteration and mineralization events. Influx of such fluids could be related to episodic fluid overpressure, resulting in dilution and cooling of the metalliferous fluid, causing deposition of metals transported as metal chloride complexes.  相似文献   

Geology of Santa Rita Coal Basin, Rio Grande do Sul, Brazil     

Z.C. Corrêa Da Silva  C.A. Bortoluzzi  M. Cazzulo-Klepzig  M.E. Dias-Fabricio  M. Guerra-Sommer  M. Marques-Toigo  P.S.G. Paim  A.E.M. Piccoli  B.C. Silva Filho 《International Journal of Coal Geology》1984,3(4):383-400

Data on the sedimentology, stratigraphy, palynology, coal petrography and geochemistry of the Santa Rita Coal Basin, Rio Grande do Sul, Brazil, are presented. The investigations were carried out on samples obtained from drill cores of the sedimentary rocks of Tubarão Supergroup, Lower Permian of Paraná Basin.The sequence comprises more than 10 coal layers, three sets of which — SR₁, SR₂ and SR₃ — are correlated with the SB+MB, I₁F and I₂B+I₃B coal seams, respectively, of the Charqueadas Coal Basin, southwest of Santa Rita. The lower, as well as the upper contacts of the sedimentary sequences are transitional and very difficult to trace.The Itararé sequences (basal group) comprise pelites, conglomerates and sandstones. The pelites are the most representative lithologies. The overlying Rio Bonito Formation comprises pelites and coal seams with subordinate para- conglomerates.Palynological analysis has unravelled a rich microfloristic association with a predominance of specimens related to the Infraturma laevigati, apiculati and cingulicavati of the Turma Triletes (Pteridophyta) either in the coal seams or in the associated rocks. Monosaccites, Disaccites and Striatiti (Gymnospermae) are accessory forms in the palynological assemblage. Botryococcus and algae-like elements are less abundant.Comparative studies of cuticular fragments collected from boreholes N₃ and P₄ showed better preservation and greater concentration in the latter, which may indicate that borehole N₃ is located closer to the margin of the swamp.Reflectance measurements ranging from 0.43 Rr% to 0.50 Rr% allow the coal seams to be classified as sub-bituminous B and A, according to the ASTM classification. Microlithotype analyses have shown the predominance of carbominerite, trimacerite and vitrite. Vitrinite is the most prominent maceral group (20–50%), inertinite and exinite are subordinate. The mineral content is about 40%.Results from geochemical analyses, from either coal or associated pelites, show the association of boron and vanadium with the organic matter; gallium is related to the inorganic material.The available sedimentological, palaeontological and petrographical data suggest a paludal environment related to swamps and the coal seams present characteristics of “reed” moor limnotelmatic facies of an authochthonous/hypautochthonous origin.  相似文献   

The response of mercury (Hg) transformation in soil to sulfur compounds and sulfur-rich biowaste application     

Jiřina Száková  Andrea Burešová  Lukáš Praus  Mercedes García-Sánchez  Zlata Holečková  Jiří Gabriel  Jiřina Sysalová  Rostislav Červenka  Josef Komárek  Slávka Grohová  Pavel Tlustoš 《Environmental Earth Sciences》2016,75(7):584

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Natural iron-containing blue and colorless euclase studied by electron paramagnetic resonance     

K. J. Guedes  K. Krambrock  M. V. B. Pinheiro  L. A. D. Menezes Filho 《Physics and Chemistry of Minerals》2006,33(8-9):553-557

Natural blue and colorless rare-gem mineral specimens of euclase from Brazil are investigated by electron paramagnetic resonance (EPR). Angular dependences of Fe³⁺ EPR spectra in three mutually perpendicular crystal planes are analyzed revealing g and D tensors with significant low-symmetry effects, as for example, the high asymmetry parameter E/D = 0.28. Fourth-order degree Stevens parameters are also included in analysis. The anisotropy of both g and D tensors is consistent with Fe³⁺ substituting for Al³⁺ ions in strongly distorted AlO₅(OH) octahedra in which the oxygen distances range from 1.85 to 1.98 Å. Fe³⁺ is not responsible for the blue color because colorless and blue euclase show nearly the same Fe³⁺ concentration as measured by EPR. However, total iron content in blue sample is much higher than in the colorless one suggesting that the existing model that Fe²⁺–Fe³⁺ intervalence charge transfer transition may explain the blue color of euclase.  相似文献   

The big picture of field hydrology studies in Brazil     

Davi C. D. Melo  Jamil A. A. Anache  Cristiano das N. Almeida  Jaqueline V. Coutinho  Geraldo M. Ramos Filho  Lívia M. P. Rosalem 《水文科学杂志》2020,65(8):1262-1280

ABSTRACT