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Keays R.R.,Monash University | Keays R.R.,Laurentian University | Lightfoot P.C.,Vale Inc.
Mineralium Deposita | Year: 2010

Process models for ore formation in magmatic Ni-Cu-platinum group element (PGE) sulfide systems require that S saturation is achieved in a mafic-ultramafic magma. Traditional models explain the achievement of S saturation or sulfide saturation either by the addition of crustal S, by the felsification of the magma by crustal contamination, or by mixing between primitive and evolved magmas. Which process matters most is important to industry-oriented exploration models where crustal S sources are believed to be encouraging features of a metallotect. Studies of the Siberian Trap flood basalts at Noril'sk have demonstrated that chalcophile element depletion is linked to assimilation of silica-rich crust, but it is less clear whether this contaminant contained an appreciable amount of S. At Noril'sk, the Ni-Cu-PGE sulfide deposits are associated with subvolcanic intrusions that were emplaced into Permian and Carboniferous sedimentary sequences rich in shales, marlstones, and evaporites. Similar to the Siberian Trap basalts, the Deccan Trap contains a volumetrically important suite of crustally contaminated tholeiitic basalts. We present new PGE data for samples from a stratigraphic sequence of basalts from the southern Deccan province. Two of the formations in this sequence (the Bushe and Poladpur Formations) have geochemical signatures indicative of a wide degree of crustal contamination of a magma type that gave rise to the stratigraphically higher Ambenali Formation (a product of transitional midocean ridge basalt magmatism). There are no known deposits or occurrences of Ni-Cu-PGE sulfides associated with subvolcanic intrusions in the Deccan province. Despite the fact that the Bushe Formation exhibits a stronger crustal contamination signature than the most contaminated Siberian Trap basalt formations, and the Poladpur lavas are also strongly crustally contaminated, the Bushe and Poladpur basalts are undepleted in Ni, Cu, or PGE. This indicates that the contaminated Deccan Trap lavas did not achieve S saturation. This, in turn, places constraints on the potential of the Deccan Trap in southern India to host significant magmatic sulfide deposits. Conversely, this observation also indicates that an S-rich crustal contaminant is required for the genesis of magmatic Ni-Cu-PGE sulfide deposits. © 2009 Springer-Verlag.


Li J.,McMaster University | Yang Q.M.,Vale Inc. | Zhitomirsky I.,McMaster University
Nanoscale Research Letters | Year: 2010

Manganese dioxide nanofibers with length ranged from 0. 1 to 1 μm and a diameter of about 4-6 nm were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors were fabricated by impregnation of the manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNT) into porous Ni plaque current collectors. Obtained composite electrodes, containing 85% of manganese dioxide and 15 mass% of MWCNT, as a conductive additive, with total mass loading of 7-15 mg cm -2, showed a capacitive behavior in 0. 5-M Na 2SO 4 solutions. The decrease in stirring time during precipitation of the nanofibers resulted in reduced agglomeration and higher specific capacitance (SC). The highest SC of 185 F g -1 was obtained at a scan rate of 2 mV s -1 for mass loading of 7 mg cm -2. The SC decreased with increasing scan rate and increasing electrode mass. © The Author(s) 2010.


Marin T.,Vale Inc. | Utigard T.,University of Toronto
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2010

The rate of deoxidation of molten copper during top blowing with various reducing gases has been investigated using thermogravimetry. It was observed that the rate of deoxidation increases with an increasing flow rate of H 2 or CO and that H2 is a more effective reducing reagent than CO. The rate of deoxidation using methane was measured for O 2/CH4 ratios from 1.5 to 2.0. As expected, the deoxidation rate decreased with an increasing O2/CH4 feed ratio because the flame became less reducing. For all tests, initially there is a linear decrease in mass as oxygen is removed. However, for some experiments, after some time, a sudden acceleration in the rate of mass loss occurs. Using video and X-ray imaging, it was found that this pattern corresponded to gas evolution from within the molten copper. This finding can be explained by the sudden water vapor evolution because the hydrogen dissolved in the copper reacts with the remaining oxygen, and 'boiling' takes place, leading to an enhanced stirring of the copper. © The Minerals, Metals & Materials Society and ASM International 2010.


Wang Y.,McMaster University | Min Yang Q.,Vale Inc. | Zhitomirsky I.,McMaster University
Materials and Manufacturing Processes | Year: 2011

Chemical and electrochemical impregnation methods have been developed for the fabrication of manganese dioxide electrodes for electrochemical supercapacitors using Ni plaques as current collectors. The methods enabled the synthesis of manganese dioxide in-situ in pores of Ni plaques. The chemical method was based on the reduction of KMnO4 solutions with isopropanol. Cathodic galvanostatic method and reverse pulse electrosynthesis method were investigated for electrochemical impregnation. The material loading was varied by the variation of the number of the dipping-reduction procedures in the chemical precipitation method or by variation of charge passed in the electrochemical methods. The microstructures of the electrodes prepared using different methods were studied by scanning electron microscopy (SEM). The electrochemical behavior of the electrodes was studied using cyclic voltammetry and impedance spectroscopy. The electrodes exhibited capacitive behavior in the 0.5M Na 2SO4 lectrolyte in a voltage window of 0-0.9V. The results obtained by different methods were compared. The chemical precipitation method offered the advantage of higher specific capacitance, whereas electrochemical methods allowed higher material synthesis rate. The highest specific capacitance of 236F g-1 was obtained at a scan rate of 2mV s-1. The specific capacitance decreased with increasing scan rate. Testing results showed that the electrodes prepared by chemical and electrochemical in-situ precipitation methods can be used for application in electrochemical supercapacitors. Copyright © Taylor & Francis Group, LLC.


Perozzi L.,Center Eau Terre Environnement | Gloaguen E.,Center Eau Terre Environnement | Rondenay S.,Massachusetts Institute of Technology | McDowell G.,Vale Inc.
Journal of Applied Geophysics | Year: 2012

Modeling of grades is a key step and the major source of error in appraisal stage of mining projects. We used a geostatistical approach to explicitly integrate seismic travel time data, as well as acoustic and core logging data into the estimation of nickel grades in the Voisey's Bay deposit. Firstly, the crosshole seismic travel times are inverted using a stochastic tomographic algorithm. This algorithm allows for the inclusion of acoustic log data and seismic covariance into the inverse problem, leading to high-resolution velocity tomographic images of the orebody. Secondly, grade realizations are generated using a Bayesian sequential Gaussian simulation algorithm, which integrates the ore grades measured on the core logs and the previously inverted tomographic data. The application of the presented method to the Voisey's Bay deposit yields an improved knowledge of the geology setting and generates grade models with realistic spatial variability compared to conventional methods. © 2011 Elsevier B.V.

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