Visualization of trace-element zoning in fluorapatite using BSE and CL imaging, and EPMA and μPIXE/μPIGE mapping

Abstract

In this paper, zonation patterns of trace elements in fluorapatite are discussed that were visualized using four analytical techniques, namely back-scattered electrons (BSE) and cathodoluminescence (CL) imaging, electron probe micro-analysis (EPMA), and micro-proton-induced X-ray/ gamma ray emission (μPIXE/μPIGE) mapping. Each method demonstrates the in-grain compositional variations in a slightly different way. Both BSE and CL provide qualitative data, and the internal textures are displayed in most detail. Additionally, CL points to specific elements enriched in certain growth zones. Qualitative EPMA maps show detailed zonation patterns for specific elements (with high spatial resolution), which are in general correspondence with the patterns observed in BSE and CL images. The μPIXE/μPIGE maps are fully quantitative and the detection limits are relatively low compared to EPMA mapping. In present spot measurements μPIXE demonstrates lower detection limits than EPMA, however, the latter could be considerably improved by extending the acquisition times. There is no significant overlap of REE (rare earth elements) peaks in the acquired μPIXE energy spectra, however, when multiple REEs are present with sufficiently high concentrations, peak deconvolution may pose some difficulties. Spatial resolution of μPIXE/μPIGE images is not sufficiently high to reflect minor textural features, which also result from the greater interaction depth of the proton beam. However, major growth zones are distinguishable. Even though each method has their advantages and limitations, when applied together, they provide an almost complete characterization of compositional variability in trace-element-bearing minerals.

REE Redistribution Textures in Altered Fluorapatite: Symplectites, Veins, and Phosphate-Silicate-Carbonate Assemblages from the Nolans Bore P-REE-Th Deposit, Northern Territory, Australia

“…The sharp peaks at ca. 600 and 630 nm most likely correspond to Sm 3þ , and the wide peak at 450 nm corresponds to Ce 3þ (Waychunas 2002, Gros et al 2016. Abbreviations: pAp -primary fluorapatite; sAp -secondary fluorapatite; rp -REE-phase.…”

Trace Element Analysis of Minerals in Magmatic-Hydrothermal Ores by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry: Approaches and Opportunities

“…Scales in counts per second (×10 3 ). Measured isotopes: 118 Sn, 182 W, 27 Al, 89 Y, 75 As, 56 Fe, 238 U, 47 Ti, 90 Zr, 45 Sc, 51 V, 140 Ce, 146 Nd, 93 Nb, 165 Ho, 175 Lu, 178 Hf.…”

“…This may be investigated by integrated use of LA-ICP-MS and EBSD studies. Although not using LA-ICP-MS, the multi-technique study of trace-element zoning in fluorapatite using BSE and CL imaging, and EPMA and µPIXE/µPIGE mapping [165] is exemplary of the kind of approach destined to become more common in the future.…”

GGR Biennial Critical Review: Analytical Developments Since 2014

“…Gros et al . () also showed the utility of combining several complementary methods. Here, electron‐based techniques (EPMA, BSE imaging and cathodoluminescence) were combined with accelerator‐based micro‐PIXE and micro‐PIGE to visualise the zonation patterns of trace elements in fluoroapatites.…”

“…EPMA generally has better spatial resolution but for a limited number of elements, while PIXE maps have a lower spatial resolution but include a larger number of elements at lower detection limits. Gros et al (2016) also showed the utility of combining several complementary methods. Here, electron-based techniques (EPMA, BSE imaging and cathodoluminescence) were combined with accelerator-based micro-PIXE and micro-PIGE to visualise the zonation patterns of trace elements in fluoroapatites.…”