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Johannesburg, South Africa

Andrews L.,Anglo Research | Andrews L.,University of Pretoria | Pistorius P.C.,University of Pretoria | Pistorius P.C.,Carnegie Mellon University
Transactions of the Institutions of Mining and Metallurgy, Section C: Mineral Processing and Extractive Metallurgy | Year: 2010

Base metals (nickel, copper and cobalt) are recovered as part of the smelting and refining process operated by Anglo Platinum in South Africa. This study focuses on the losses of these metals to furnace slag and the effect of changing the furnace feed to include or exclude recycled oxidising converter slag. A combination of electron microbeam and Mössbauer techniques were used to characterise the base metal distribution in the slag, the variation of losses with depth in the slag bath, and the oxygen activity in the slag. Base metal dissolution into the slag is underestimated if bulk matte-slag equilibrium is assumed; predictions are closer to the observed extent of dissolution if equilibrium between entrained matte and slag is assumed, for oxygen activity controlled by the Fe3+(slag)/Fe2+(slag) or FeO(slag)/Fe(matte) buffers. © 2010 Maney Publishing.

Vanhaecke F.,Ghent University | Resano M.,University of Zaragoza | Koch J.,ETH Zurich | McIntosh K.,Anglo Research | Gunther D.,ETH Zurich
Journal of Analytical Atomic Spectrometry | Year: 2010

Owing to the shorter time interval during which energy is delivered to the sample material, femtosecond (fs) laser ablation is preferable over nanosecond laser ablation for metallic samples. In this project, the influence of various laser parameters - beam diameter, repetition rate and laser fluence - on the ablation of Pb as a heavy metallic matrix using an infrared (λ = 795 nm) fs-LA system (150 fs pulse duration) was studied. The merits of Ar and He as carrier gases were compared and as He did not provide a substantial improvement in the limits of detection, while deposition of sample material on the window of the ablation chamber was more pronounced, Ar was selected for all further measurements. The effect on the ICP caused by the introduction of various amounts of sample aerosol was studied by monitoring the signal intensity for 38Ar+. It was shown that maximizing the amount of sample ablated and thus, the amount of sample aerosol introduced into the ICP, did not result in maximum sensitivity, which was rather obtained under 'compromise' conditions. Subsequently, femtosecond LA-quadrupole-based ICP-mass spectrometry (ICP-MS) was used for the determination of traces of the platinum group metals (PGMs) Rh, Pd, Ru, Ir and Pt and of Au in Pb buttons obtained by fire assay of platiniferous ore reference materials. The signal of 204Pb + was used as an internal reference, correcting for variations in the laser ablation and transport efficiencies and in the instrument's sensitivity. The spectral interferences established for some of the target nuclides due to the occurrence of Pb2+ ions were successfully overcome by pressurizing the reaction cell with NH3. Quantification versus a calibration curve constructed on the basis of the results obtained for matrix-matched standards (> 99% Pb) provided excellent accuracy, superior to those obtained using nanosecond LA-ICP-MS. Also the limits of detection were improved by a factor ranging between 3 and 10 and are <0.010 μg g -1 for the most important PGMs (Rh, Pd, Pt) and Au. Several measures, such as the use of a large ablation cell and housing up to 10 Pb buttons, were taken to increase the sample throughput. In the same context, day-to-day reproducibility of the calibration curve was also examined. When recording a 'fresh' calibration curve every day, the average bias between the experimental results and the corresponding reference values was established to be <2.5% for every target element. When using one calibration curve during three consecutive days, the bias still remains <10%, while the sample throughput is increased and analysis of several tens of buttons per day is feasible (10-15 min total analysis time per sample). © The Royal Society of Chemistry 2010.

Tonzetic I.,Anglo Research | Dippenaar A.,Kumba Iron Ore
Minerals Engineering | Year: 2011

An alternative to the traditional quantification of iron ore sinter mineralogy is presented through the use of QEMSCAN instrumentation. The classification of minerals by QEMSCAN is based on chemical composition whilst the traditional classification of iron ore sinter mineralogy, through point counting, is based on morphology. The classification of iron ore sinter minerals through XRD is based on crystal structure. Advantages of the QEMSCAN technique include the ability to distinguish magnesio ferrites from calcio magnetites and the fact that calcium ferrite and silico-ferrite of calcium and aluminium (SFCA) distinction is not dependant on the sectioning of the sample mount. © 2011 Elsevier Ltd. All rights reserved.

van Staden A.,University of Johannesburg | van Staden A.,Anglo Research | Zimmermann U.,University of Johannesburg | Zimmermann U.,University of Stavanger | And 5 more authors.
Journal of the Geological Society | Year: 2010

The results of detrital zircon U-Pb geochronology suggest a maximum depositional age of 485 ± 7.2 Ma for a glacial diamictite from the Sierra del Volcán in eastern Argentina (Tandilia System). Earlier interpretations associated the deposit with the Neoproterozoic 'snowball Earth' hypothesis. The data allow direct correlation, for the first time, between Early Palaeozoic deposits in both South America and South Africa connecting the glacial deposits from southern Bolivia to central Argentina with those in South Africa (Pakhuis Formation). On the basis of these results, a new distribution map of glacial cover, corresponding to the Hirnantian stage, can be developed. © 2010 Geological Society of London.

Viljoen F.,University of Johannesburg | Viljoen F.,De Beers Geoscience Center | Dobbe R.,FEI Electronic Optics BV | Harris J.,University of Glasgow | Smit B.,Anglo Research
Lithos | Year: 2010

Although diamonds of eclogitic paragenesis are commonly encountered in the productions of many Southern Africa kimberlites, the nature and evolution of the protolith to eclogitic diamonds are still poorly understood. There is some evidence that these protoliths (and possibly also the diamonds) may be related to subduction of oceanic crust, although this is not a universally accepted view. In order to further investigate the protolith/diamond relationship, garnets and (in some cases) clinopyroxene inclusions in 23 diamonds from Premier mine and 16 diamonds from Finsch were analysed for their trace element composition. From both mines a strong correlation between the garnet Ca content and the chondrite-normalised rare earth element (REE) pattern is evident. Garnets with comparatively low Ca content are characterised by REE patterns which show a steady increase in abundance from light rare earths (LREE) to heavy rare earths (HREE). With increasing Ca content in garnet, the abundance of LREE (La, Ce, Pr, and Nd) as well as the middle rare earths (MREE; Sm, Eu, Gd, and Tb) progressively increases, ultimately giving the trace element pattern a distinct 'humped' appearance. Bulk-rock trace element abundance patterns have been reconstructed from measured trace element contents in garnet as well as calculated trace element concentrations in clinopyroxene, based on known clinopyroxene-garnet partition coefficients (Harte and Kirkley, 1997). At both Premier and Finsch, the low-Ca group samples (2.6 to 5.0. wt.% CaO in garnet) are LREE depleted, and have relatively flat calculated bulk-rock trace element abundance patterns at approximately 10 times chondrite concentrations, but with marked positive Sr and negative Zr anomalies. The intermediate-Ca group samples (5.2 to ~9. wt.% CaO in garnet) are LREE depleted, show Sr and Zr anomalies, have somewhat higher concentrations of Zr and MREE, and have HREE contents that overlap with the low-Ca group (Fig. 6). High-Ca group samples (~. 9 to 14.8. wt.% CaO in garnet) are LREE depleted, show Sr and Zr anomalies, are MREE-enriched, and have HREE contents that are slightly less than the low- and intermediate-Ca group samples. Based on both the calculated bulk eclogite trace element abundances and their patterns, as well as previously published radiogenic isotope data, our preferred model of protolith evolution for the eclogitic diamonds from Premier and Finsch is one in which both the major and trace element chemistry of the inclusions are ultimately inherited from low-pressure oceanic protoliths, consisting of varying mixtures of oceanic basalt. +. cumulate gabbro for diamonds from both Premier and Finsch. Of particular importance in the current data are the presence of marked negative Zr anomalies, marked positive Sr anomalies, and a general absence of Eu anomalies in all compositional groupings. The Zr anomaly can arise in reconstructed bulk eclogite trace element abundance patterns if rutile is not included in the calculations, but the Sr anomalies (coupled with an absence of Eu anomalies) can only be explained through the mixing of oceanic gabbro and mid-ocean ridge basalt. The averaged eclogite bulk trace element compositions for Premier and Finsch are also markedly similar to that of clinopyroxene in a typical cumulate gabbro, and a role for cumulate clinopyroxene in protolith evolution may therefore also be inferred. It is likely that prior to and during diamond crystallisation, the major and particularly the trace element compositions of the high-pressure eclogite source rock to these diamonds may have been slightly modified by metasomatic fluids and melts. However large-scale fluid- or melt-related metasomatic processes are not indicated. © 2010 Elsevier B.V.

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