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61.
Maria Inês C. Monteiro Marcos Paulo A. Lavatori Nilza Maria M. de Oliveira 《Geostandards and Geoanalytical Research》2003,27(3):245-249
A method involving gold extraction into isobutyl methyl ketone (IBMK), after partial dissolution with aqua regia , with determination by electrothermal atomic absorption spectrometry is described. The pyrolysis and atomisation temperatures were optimized using a pyrolytic graphite forked platform. The stability study of gold in isobutyl methyl ketone extract indicated that closed polypropylene containers (3% absorbance measurement changes) were better than both open polypropylene and closed glass containers over periods of up to 22 hr. Satisfactory recoveries of 99 and 102% were obtained when Au, in the IBMK extracts from CH-3 and MA-2 reference materials, were determined after storage of the extracts in closed polypropylene containers for 22 hr, respectively. 相似文献
62.
M. Marconi V. Ripepi S. Bernabei A. Ruoppo M. J. P. F. G. Monteiro J. P. Marques F. Palla S. Leccia 《Astrophysics and Space Science》2010,328(1-2):109-111
The Herbig Ae star PDS2 was found to pulsate as a Pre-Main-Sequence delta Scuti star on the basis of R.E.M. telescope photometry. From the frequency analysis we have found four significant pulsation frequencies. We discuss these results and their interpretation through the adoption of nonradial pulsation models, deriving the first information on the intrinsic properties of this young star. 相似文献
63.
Water-Tank Studies of Separating Flow Over Rough Hills 总被引:1,自引:1,他引:0
J. B. R. Loureiro A. S. Monteiro F. T. Pinho A. P. Silva Freire 《Boundary-Layer Meteorology》2008,129(2):289-308
The present work investigates the lower boundary condition for flows over a steep, rough hill. Simple asymptotic arguments
together with the mixing-length hypothesis are used to derive a local analytical solution that is tested against three different
flow conditions. In all, 36 velocity profiles are compared with the proposed expression. The experiments were carried out
in a water channel and velocity measurements were made through laser Doppler anemometry. The extent of separated flow was
made to vary as a function of the roughness and the Reynolds number. The analysis includes regions of attached as well as
separated flow. In particular, the solution of Stratford is studied at the points of separation and re-attachment and found
to apply equally well in rough walls. 相似文献
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68.
Isotope geochemistry of the mafic dikes from the Vazante nonsulfide zinc deposit, Brazil 总被引:2,自引:0,他引:2
M. Babinski L.V.S. Monteiro A.H. Fetter J.S. Bettencourt T.F. Oliveira 《Journal of South American Earth Sciences》2005,18(3-4):293-304
The Vazante Group, located in the northwestern part of Minas Gerais, hosts the most important zinc mine in Brazil, the Vazante Mine, which represents a major known example of a hypogene nonsulfide zinc deposit. The main zinc ore is represented by willemite and differs substantially from other deposits of the Vazante-Paracatu region, which are sulfide-dominated zinc-lead ore. The age of the Vazante Group and the hosted mineralization is disputable. Metamorphosed mafic dikes (metabasites) that cut the metasedimentary sequence and are affected by hydrothermal processes recently were found and may shed light on the geochronology of this important geological unit. Zircon crystals recovered from the metabasites are xenocrystic grains that yield U–Pb conventional ages ranging from 2.1 to 2.4 Ga, so the basement of the Vazante Group is Paleoproterozoic or has metasedimentary rocks whose source area was Paleoproterozoic. Pb isotopes determined for titanite separated from the metabasites have common, nonradiogenic Pb compositions, which prevents determination of their crystallization age. However, the Pb signatures observed for the titanite crystals are in agreement with those determined for galena from the carbonate-hosted Zn–Pb deposits hosted by the Vazante Group, including galena from minor sulfide ore bodies of the Vazante deposit. These similarities suggest that the metalliferous fluids that affected the metabasites may have been those responsible for galena formation, which could imply a similar lead source for both nonsulfide and sulfide zinc deposits in the Vazante–Paracatu district. This common source could be related to deep-seated, basin-derived, metalliferous fluids associated with a long-lived hydrothermal system related to diagenesis and deformation of the Vazante Group during the Neoproterozoic. 相似文献
69.
Are some of the deep crustal conductive features found in SW Iberia caused by graphite? 总被引:1,自引:0,他引:1
Fernando A. Monteiro Santos António Mateus Jaume Pous 《Earth and Planetary Science Letters》2002,201(2):353-367
Recent results obtained from two-dimensional inversion of magnetotelluric (MT) data acquired in SW Iberia reveal high-conductive features at the middle-lower levels of the crust. The top of these anomalous structures correlates very well with the depth (10-13 km) of an important seismic interface that has been interpreted as a regional detachment horizon. Very shallow and relatively narrow conductors in the Ossa Morena Zone appear to correspond to small-scale fluid-deposited graphite systems in the preorogenic metasedimentary sequences. Some of the midcrustal conductors can be ascribed to graphite-bearing thrust zones, the formation of graphite with variable crystallinity being a consequence of Variscan shearing processes. Deep-seated conductors are tentatively interpreted as a result of relatively continuous, highly crystalline grain-boundary graphite films presumably preserved in basement, granulite(?) rocks. Assuming that graphite occurs as interconnected films, calculations indicate that a fraction of 0.006-0.02% of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of MT models. The role of graphite on the thermal behaviour of the crust is also discussed. The results show that low contents of graphite do not significantly change the thermal behaviour of earth materials. 相似文献
70.
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 δDH2O 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