Applicability of handheld X-Ray fluorescence spectrometry in the exploration and development of carbonatite-related niobium deposits: a case study of the Aley Carbonatite, British Columbia, Canada

Abstract

This study evaluates the suitability of portable (handheld) X-Ray fluorescence spectrometry (pXRF) in the exploration for Aley-type ‘hard-rock’ (primary) carbonatite-hosted Nb deposits. The assessment consists of comparisons between: (1) results of pXRF analyses on selected pulp samples and results of analyses of the same pulps using traditional laboratory methods; (2) results of averaged, multiple pXRF spot field analyses performed directly on 10 to 15 cm long pieces of core (before pulverization) compared with those of traditional laboratory analyses of the same pieces of core after pulverization; and (3) results of a manual core scanning method compared with the results of conventional analytical methods of the pulps of the corresponding scanned sections. A strong correlation exists between pXRF measurements on pulps and laboratory methods for most specialty metals, such as Nb (r 2 = 0.99), La (r 2 = 0.97), Ce (r 2 = 0.67), Y (r 2 = 0.93), and P (r 2 = 0.89); however, the values of r 2 for Pr and Nd are 0.19 and 0.38, respectively. As expected, textural heterogeneities within sample intervals reduced the quality of pXRF results when multiple spot readings were taken directly on the core. Nevertheless, the data can still be used to identify carbonatite-related Nb (± other specialty metal mineralization) and delimitate potentially economically significant zones within it. The core scanning reduced the degree of variation associated with spot analyses. Scanning is useful during the early exploration stages, but provides data limited by the inability of the operator to maintain constant scanning speed. The scanning results correlate with laboratory methods for Nb (r 2 = 0.88), Th (r 2 = 0.80), Fe (r 2 = 0.84), Sr (r 2 = 0.74), Ba (r 2 = 0.73), Y (r 2 = 0.59), and Zn (r 2 = 0.75). The values of r 2 for La, Ce, Pr, and Nd were only 0.31, 0.26, 0.01 and 0.03, respectively, suggesting that concentrations of these elements were too low, and/or that the light rare earth elements (LREEs) were present not only in the crystal structure of fersmite, pyrochlore and apatite, but also in minor or accessory minerals such as REE-bearing fluorocarbonates or zircon erratically distributed throughout the core. Portable XRF is a robust tool facilitating exploration-related decision-making in the field, assuming that elements of interest such as Nb are present in concentrations within the analytical range of the instrument. The pXRF core scanning reduces the need for sample preparation (no pulps) and can be done directly on the drill-site, but the precision and accuracy of the data are reduced relative to laboratory and pXRF pulp analyses. The multiple spot analyses (no pulps) approach is good for instant verification of unknown, potentially ore-bearing minerals and for analysing discrete homogeneous features, layers, veins, etc; however, under normal circumstances this method is inferior to pulp analyses in precision and accuracy, and to scanning for determining average grade of core intervals.

The Influence of Spectral Interferences on Critical Element Determination with Portable X-Ray Fluorescence (pXRF)

“…The potential of quick in situ analysis coupled with the instant display of results makes this technology particularly appealing for the mining industry. Most of the mineral resources-related pXRF projects have focussed on base and precious metals and have shown that this technology, when appropriately used, may yield data of sufficient quality for exploration and geochemical comparison [7][8][9][10][11][12][13][14][15].…”

“…However, portable XRF spectrometers have proven suitable to detect REEs, Ta, and Nb in phosphates and carbonatites [13][14][15], W, Nb, Ta, La, Ce, and Zr in Sn-W ore-bearing granites [20], Ta and Zr in soil overlying granites [12], and P, Ba, Nb, V, Zr, and Y in various mafic to felsic igneous rocks [7,[21][22][23][24]. Consequently, critical elements can be detected and reliably quantified in geological materials devoid of interfering elements or when enriched.…”

Economic Geology Models 2. Tantalum and Niobium: Deposits, Resources, Exploration Methods and Market – A Primer for Geoscientists

“…It is expected that new deposits will be discovered as exploration methods for Nb and Ta are optimized. Some recent and significant breakthroughs include customizing and optimizing the use of portable X-Ray Fluorescence to provide sufficiently accurate and precise chemical analyses for specialty metals directly in the field (Simandl et al 2014), optimization of indicator mineral-based exploration methodology to detect Nb-Ta mineralization (e.g. Mackay and Simandl 2015;Mackay et al 2016), and the use of exploration biogeochemistry (Fajber et al 2015).…”

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

“…In one of a series of publications, Simandl et al 119 reported the use of hand-held XRF instrumentation for the exploration of primary carbonatite-hosted niobium deposits. In one of a series of publications, Simandl et al 119 reported the use of hand-held XRF instrumentation for the exploration of primary carbonatite-hosted niobium deposits.…”