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São Paulo, Brazil

Cabral A.R.,Clausthal University of Technology | Eugster O.,University of Bern | Brauns M.,University of Tubingen | Lehmann B.,Clausthal University of Technology | And 5 more authors.
Geology | Year: 2013

New analytical developments have made radiogenic helium (4He) applicable to archeological gold artifacts for age determinations. Here we report the application of the U/Th-4He method to the direct dating of gold from the historically important gold deposit in Diamantina, Minas Gerais, Brazil. The U/Th-4He age of 515 ± 55 Ma for the Diamantina gold is corroborated by a new U/Pb age of 524 ± 16 Ma for rutile recovered from auriferous pockets. These ages tie the Diamantina gold mineralization to the Brasiliano orogenic event, in the context of the Gondwana amalgamation. Our results indicate that U/Th-4He dating of gold is possible, opening new perspectives for the dating of gold deposits without assuming contemporaneity between gold and datable hydrothermal minerals.

Binotto R.B.,Federal University of Rio Grande do Sul | Saldanha D.L.,Federal University of Rio Grande do Sul | Dias A.R.A.,Votorantim Metais | Perrota M.M.,Servico Geologico do Brazil CPRM
Pesquisas em Geociencias | Year: 2015

A series of spectral analysis was made with samples of Eopaleozoic sedimentary rocks affected by hydrothermal alteration associated with occurrences of copper in Uruguai Mine (Minas do Camaquã, Rio Grande do Sul State, Brazil). The database included spectral range visible, near infrared and shortwave (350-2500 nm) obtained from measurements of portable spectroradiometer ASD FieldSpec-3 High-Resolution. The mineralogical interpretation with spectral signatures was conducted with a support by The Spectral Geologist (TSG™ Pro) software, which allows a mineral phases discrimination present by comparing the absorption features in the mineral analysis with similar features of a spectral reference library spectrum. Spectral analysis from studied area samples allowed identified these main minerals: kaolinite, illite, chlorite, hematite and goethite. The mineral assemblages identified wereconsistent with hydrothermal alteration under conditions of low sulphur epithermal described in previous studies in this region. The results supported a potential use of reflectance spectroscopy in mineral exploration programs, especially in the early stages, even in areas with little favorable physiographic conditions. © 2015, Universidade Federal do Rio Grande do Sul. All rights reserved.

Misi A.,Federal University of Bahia | Kaufman A.J.,University of Maryland University College | Azmy K.,Memorial University of Newfoundland | Dardenne M.A.,University of Brasilia | And 2 more authors.
Geological Society Memoir | Year: 2011

The Neoproterozoic successions of the São Francisco Craton are primarily represented by the Bambuí and Una groups, deposited in cratonic epicontinental basins, and by the Vazante and Vaza Barris/Miaba groups, which accumulated on passive margins on the edges of the craton. The epicontinental basins comprise three megasequences: glaciogenic, carbonate platform (marine) and dominantly continental siliciclastics. Possible correlative sequences are observed in the passive margin deposits. At least two major transgressive-regressive sea-level cycles occurred during the evolution of the carbonate megasequence, which lies above glaciomarine diamictites of probable early Cryogenian (i.e. Sturtian) age. C, O, Sr and S isotope trends from analyses of well-preserved samples, together with lithostratigraphic observations, provide reasonable correlations for most of the Neoproterozoic successions of the São Francisco Craton. The 87Sr/ 86Sr record of these successions, ranging from 0.70769 to 0.70780, supports the proposed correlation with the Bambuí, Una and Vaza/Barris successions, and with the basal units of the Vazante Group. In addition, C-isotope positive excursions ranging from +8.7 to +14‰ and negative excursions from -5.7 to -7‰ VPDB in the Bambuí, Una and Vaza-Barris successions provide key markers for correlations. The precise ages of the sedimentation in these successions remains a matter of debate, but organic shales of two units of the Vazante Group have been dated by Re-Os techniques in two different laboratories, both yielding Mesoproterozoic ages. The Neoproterozoic and Mesoproterozoic successions preserve significant glaciogenic deposits. © The Geological Society of London 2011.

Van Deursen C.,Votorantim Metais
TMS Light Metals | Year: 2015

The Alumina Rondon refinery will have a production capacity of 3.0 million tons of smelter grade alumina per year. For this production, approximately, 11.0 million tons of bauxite Run of Mine (RoM) will be necessary. This bauxite must be washed prior being fed in the refinery, and so, the beneficiation plant will dispose 3.0 million tons (dry basis) of bauxite reject. The moisture of this material, at the moment of disposal, may vary from 88% to 25%, depending on the dewatering method. The moisture is a conditionant to the disposal, ranging from discharging the pulp in tailing ponds or back filling mined areas with mechanical dewatered reject. This study evaluated different ways of treatment, handling and disposal of the reject. The comparison was made in terms of Capital Expenditure (CapEx) and Operational Expenditure (OpEx). The compared indicator is the Net Present Value of the accumulated Free Cash Flow (FCF). This comparison allows to evaluate the best financial solution for the life of the project. The evaluated scenarios included combinations between ways of dewatering the reject (natural settling, thickening, supperfloculaltion and pressfiltering) and ways of diposing it (tailing ponds, heightened tailing ponds and mine back fill). The superflocculation option has the lowest CapEx while back filling mined areas with press filtered reject saves 30% of the value of the base case scenario: direct disposal in tailing ponds without previuos thickening.

Van Deursen C.,Votorantim Metais
TMS Light Metals | Year: 2015

The Alumina Rondon project consists of a bauxite mine, beneficiation plant and an alumina refinery, along with its associated logistics. It will be installed in the Rondon do Para municipality in the Para state - northern Brazil. The refinery production capacity is three million tons of alumina per year. For this production, 12 million tons of ROM will be beneficiated, resulting in 8 million tons of washed bauxite. The beneficiation process will occur in a single line plant at 1.500 tons per hour. During the early stages of the project engineering, a characterization study was conducted. Such a study consists in the evaluation and quantification several key aspects of the material needed to proper equipment sizing. To confirm the values of the laboratory scale studies, an industrial scale test was done in the operating bauxite beneficiation plant installed in the Mirai municipality located in the state of Minas Gerais - southeast Brazil. The test was done with two bulk samples obtained from two pilot scale mines. The main aspects evaluated were: product loss, product contamination and effects of residence time in the scrubber.

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