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Efficient and Accurate Identification of Platinum-Group Minerals by a Combination of Mineral Liberation and Electron Probe Microanalysis with a New Approach to the Offline Overlap Correction of Platinum-Group Element Concentrations*

Published online by Cambridge University Press:  21 July 2015

Inga Osbahr ,
Joachim Krause ,
Kai Bachmann  and
Jens Gutzmer
Inga Osbahr*
Affiliation:
Helmholtz Center Dresden—Rossendorf, Helmholtz-Institute Freiberg for Resource Technology, Halsbrücker Str. 34, D-09599 Freiberg, Germany
Joachim Krause
Affiliation:
Helmholtz Center Dresden—Rossendorf, Helmholtz-Institute Freiberg for Resource Technology, Halsbrücker Str. 34, D-09599 Freiberg, Germany
Kai Bachmann
Affiliation:
Helmholtz Center Dresden—Rossendorf, Helmholtz-Institute Freiberg for Resource Technology, Halsbrücker Str. 34, D-09599 Freiberg, Germany
Jens Gutzmer
Affiliation:
Helmholtz Center Dresden—Rossendorf, Helmholtz-Institute Freiberg for Resource Technology, Halsbrücker Str. 34, D-09599 Freiberg, Germany Department of Mineralogy, Technische Universität Bergakademie Freiberg, Brennhausgasse 14, D-09596 Freiberg, Germany
*
*Corresponding author.i.osbahr@hzdr.de
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Abstract

Identification and accurate characterization of platinum-group minerals (PGMs) is usually a very cumbersome procedure due to their small grain size (typically below 10 µm) and inconspicuous appearance under reflected light. A novel strategy for finding PGMs and quantifying their composition was developed. It combines a mineral liberation analyzer (MLA), a point logging system, and electron probe microanalysis (EPMA).

As a first step, the PGMs are identified using the MLA. Grains identified as PGMs are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that the combination of MLA, point logging, and EPMA results in the identification of a significantly higher number of PGM grains than reflected light microscopy. Analysis of PGMs by EPMA requires considerable effort due to the often significant overlaps between the X-ray spectra of almost all platinum-group and associated elements. X-ray lines suitable for quantitative analysis need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight proportions has been developed. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, indicating that the applied corrections are appropriate.

Keywords

mineral liberation analysiselectron probe microanalyzerplatinum-group elementsoverlap correctionoffline overlap factors
Type
EMAS Special Issue
Information
Microscopy and Microanalysis , Volume 21 , Supplement 5 , October 2015 , pp. 1080 - 1095
Copyright
© Microscopy Society of America 2015 

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Footnotes

*

This article is intended for the Special Issue from the EMAS 2014 Workshop on “Electron Probe Microanalysis of Materials Today – Rare and Noble Elements: from Ore Deposits to High-tech Materials”.

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