An Evaluation of the Potential for Determination of the Geographic Origin of Ruby and Sapphire Using an Expanded Trace Element Suite Plus Sr–Pb Isotope Compositions

Abstract

The geographic origin of gem corundum has emerged as one of its major value factors. Combined with gemological observations, trace element analysis is a powerful tool for the determination of corundum provenance. However, owing to similar properties and features of gem corundum from different localities, but similar geological settings, and very low levels of many trace elements in gem corundum, the determination of geographic origin remains challenging. In this study, we present trace elements compositions determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for rubies and blue sapphires from several different localities of geologically similar deposits: high-Fe amphibolite-type rubies, low-Fe marble-type rubies, and metamorphic blue sapphires. In addition, we determined Sr and Pb isotopic ratios by offline laser ablation sampling followed by thermal ionization mass spectroscopy (TIMS). By applying new and existing elemental discrimination schemes and the multivariate statistical method linear discriminant analysis (LDA), we show that, in addition to the commonly used discriminators Mg, Fe, V, Ti, and Ga, the elements Ni, Zr, Cr, and Zn show potential for geographic origin determination. Amphibolite-type rubies from different localities can be discriminated using Sr and Pb isotope ratios, whereas the discrimination of marble-type ruby and metamorphic blue sapphires is limited. Our results re-emphasize the challenge of geographic origin determination and the need for a more powerful discriminatory tool.

Editorial for Special Issue “Mineralogy and Geochemistry of Ruby”

“…This not only provides a solid foundation on the mineralogy and geochemistry involved in this gem varietal, but also presents an encompassing survey of its global deposits through historic and geological time. From this supporting synthesis, the satellite papers present their own particular points of interest that carry the ruby theme into new research territory [8][9][10][11][12][13]. Research into gem corundum, however, is a continuing process, and new aspects are already appearing since publication of the papers in the Special Issue.…”

“…Off-line laser ablation was combined with thermal ionizing mass spectrometry (TIMS) in analyzing the radiogenic isotopic compositions. These novel techniques are used in a wider study presented in this current Special Issue [10].…”

“…In terms of the wider study, Krebs et al [10] examine the usefulness of trace element and radiogenic isotopes for geographic typing for gem corundum. They stress that distinction of host lithology is more reliable than in determining a precise geographic provenance, particularly for marble-type ruby.…”

“…In the Conclusions, the authors considered that geographic differentiation of amphibolite-type rubies is fairly simple but is more challenging for marble-type rubies and metamorphic blue sapphires. They emphasize the promise of using combined isotopic and trace element fingerprints, but for precise geographic origin, more powerful discriminating tools need development [10].…”

Analytical Proof of Origin for Raw Materials

“…In combination with gemological properties, it was possible to distinguish ruby and sapphire from different deposits worldwide. Trace element chemistry and isotope ratios are used frequently to determine the geographic origin of ruby and sapphire using binary or ternary discriminating plots or multivariate linear discriminant analysis (LDA) based on various analytical tools like LA-ICP-MS, portable X-ray fluorescence (XRF), energy-dispersive XRF (EDXRF), and thermal ionization mass spectrometry (TIMS) [50][51][52][53]. Besides trace element chemistry, UV-Vis-NIR spectroscopy, Raman spectroscopy, and the study of inclusion scenes are additional tools to determine the origin of blue sapphire [54].…”