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An empirical approach for estimating reference material heterogeneity and sample minimum test portion mass for "nuggety" precious metals (Au, Pd, Ir, Pt, Ru)

Bedard L. Paul, Esbensen Kim H. et Barnes Sarah-Jane. (2016). An empirical approach for estimating reference material heterogeneity and sample minimum test portion mass for "nuggety" precious metals (Au, Pd, Ir, Pt, Ru). Analytical chemistry, 88, (7), p. 3504-3511.

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URL officielle: http://pubs.acs.org/doi/abs/10.1021/acs.analchem.5...

Résumé

Quantification of precious metal content is important for studies of ore deposits, basalt petrogenesis, and precious metal geology, mineralization, mining, and processing. However, accurate determination of metal concentrations can be compromised by microheterogeneity commonly referred to as the "nugget effect", i.e., spatially significant variations in the distribution of precious metal minerals at the scale of instrumental analytical beam footprints. There are few studies focused on the spatial distribution of such minerals and its detrimental effects on quantification of the existing suite of relevant reference materials (RM). In order to assess the nugget effect in RM, pressed powder pellets of MASS-1, MASS-3, WMS-1a, WMS-1, and KPT-1 (dominantly sulfides) as well as CHR-Pt+ and CHR-Bkg (chromite-bearing) were mapped with micro-XRF. The number of verified nuggets observed was used to recalculate an effective concentration of precious metals for the analytical aliquot, allowing for an empirical estimate of a minimum mass test portion. MASS-1, MASS-3, and WMS-1a did not contain any nuggets; therefore, a convenient small test portion could be used here (<0.1 g), while CHR-Pt+ would require 0.125 g and WMS-1 would need 23 g to be representative. For CHR-Bkg and KPT-1, the minimum test portion mass would have to be ∼80 and ∼342 g, respectively. Minimum test portions masses may have to be greater still in order to provide detectable analytical signals. Procedures for counteracting the detrimental manifestations of microheterogeneity are presented. It is imperative that both RM and pristine samples are treated in exactly the same way in the laboratory, lest powders having an unknown nugget status (in effect all field samples for analysis) can not be documented to be representing a safe minimum mass basis.

Type de document:Article publié dans une revue avec comité d'évaluation
ISSN:0003-2700
Volume:88
Numéro:7
Pages:p. 3504-3511
Version évaluée par les pairs:Oui
Date:2016
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Déposé le:17 juin 2016 15:11
Dernière modification:09 déc. 2016 15:40
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