Spatial Geochemistry: A Characterisation of Heterogeneity in Reference Materials

Abstract

Geochemical reference materials (RMs) for microbeam techniques are typically characterised by averages and dispersion statistics (e.g., standard deviation, variance) that are calculated for a number of measurements (beam shots). It is proposed that the mapping of RMs will add spatial information that better characterises the grouping and magnitudes of the heterogeneities and provides the information necessary to define a minimum analytical mass. A simple mathematical solution is proposed, which can be easily computed and understood. The analogous notions to sill and range from geostatistics are applied to the minimum analytical mass versus the relative standard deviation. To assess grouping and magnitudes of the heterogeneities, a ‘proximity number’ is computed for each average value ± ‘n’ standard deviations (magnitude). Different chemical anomalies have been simulated to demonstrate the behaviour of the proximity number. To further test the proposed spatial geochemistry concept, sulfide‐ and oxide‐bearing RMs have been selected because many are crippled with nugget effect. They have been mapped with a micro‐XRF apparatus, and results are presented for CHR‐Bkg, CHR‐Pt+, MASS‐1, MASS‐3, WMS‐1 and WMS‐1a. MASS‐1 and MASS‐3 are the most suitable RMs for microbeam techniques. Spatial geochemistry offers a new approach to better characterise reference materials.

Major Element Chemical Heterogeneity in Geo2 Olivine Microbeam Reference Material: A Spatial Approach to Quantifying Heterogeneity in Primary Reference Materials

“…Both software packages are routinely utilised by geochemists in the mineral exploration community and contain a range of features that made them suitable for this task. For instance, we were able to modulate the spatial influence of each point in ioGAS , which provided considerable control over the weighting of each analysis spot, which in turn made the task of spatial geochemical mapping of the RM (see Bédard and Néron for an introduction to the concept) easily tailored to the user's requirements.…”

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“…However, many geochemical RM development projects do not attempt a detailed quantification of material heterogeneity at fine‐scale sampling sizes appropriate for microanalytical work. Micro‐XRF was used by Bédard and Néron () to quantify heterogeneities in powdered reference materials. They used chemical maps of reference materials pressed into pellets to characterise the spatial distribution of heterogeneities in the RM, from which they could define a minimum test portion mass for representative results.…”

2015 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry and their applications

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