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Authenticity and provenance studies of copper-bearing andesines using Cu isotope ratios and element analysis by fs-LA-MC-ICPMS and ns-LA-ICPMS

Fontaine, Gisela ; Hametner, Kathrin ; Peretti, Adolf ; Günther, Detlef

In: Analytical and Bioanalytical Chemistry, 2010, vol. 398, no. 7-8, p. 2915-2928

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    Titre
    • Authenticity and provenance studies of copper-bearing andesines using Cu isotope ratios and element analysis by fs-LA-MC-ICPMS and ns-LA-ICPMS
    Auteur
    • Fontaine, Gisela. Laboratory of Inorganic Chemistry, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093, Zürich, Switzerland
    • Hametner, Kathrin. Laboratory of Inorganic Chemistry, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093, Zürich, Switzerland
    • Peretti, Adolf. GRS Gemresearch Swisslab AG, Sempacherstr. 1, P.O. Box 3628, 6002, Lucerne, Switzerland
    • Günther, Detlef. Laboratory of Inorganic Chemistry, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093, Zürich, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Analytical and Bioanalytical Chemistry, 2010, vol. 398, no. 7-8, p. 2915-2928. Springer-Verlag
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:317672
    Summary
    Whereas colored andesine/labradorite had been thought unique to the North American continent, red andesine supposedly coming from the Democratic Republic of the Congo (DR Congo), Mongolia, and Tibet has been on the market for the last 10years. After red Mongolian andesine was proven to be Cu-diffused by heat treatment from colorless andesine starting material, efforts were taken to distinguish minerals sold as Tibetan and Mongolian andesine. Using nanosecond laser ablation-inductively coupled plasma mass spectrometry (ICPMS), the main and trace element composition of andesines from different origins was determined. Mexican, Oregon, and Asian samples were clearly distinguishable by their main element content (CaO, SiO2 Na2O, and K2O), whereas the composition of Mongolian, Tibetan, and DR Congo material was within the same range. Since the Li concentration was shown to be correlated with the Cu concentration, the formerly proposed differentiation by the Ba/Sr vs. Ba/Li ratio does not distinguish between samples from Tibet and Mongolia, but only between red and colorless material. Using femtosecond laser ablation multi-collector ICPMS in high-resolution mode, laboratory diffused samples showed variations up to 3‰ for 65Cu/63Cu within one mineral due to the diffusion process. Ar isotope ratio measurements proved that heat treatment will reduce the amount of radiogenic 40Ar in the samples significantly. Only low levels of radiogenic Ar were found in samples collected on-site in both mine locations in Tibet. Together with a high intra-sample variability of the Cu isotope ratio, andesine samples labeled as coming from Tibet are most probably Cu-diffused, using initially colorless Mongolian andesines as starting material. Therefore, at the moment, the only reliable source of colored andesine/labradorite remains the state of Oregon. Figure Cu diffusion can be used to turn a plain, colorless andesine into a red gemstone. Cu and Ar isotope ratios in combination with main and trace elemental analysis can appoint andesine to thrie origin in Oregon, Mexico and Asia. In this study, red andesines sold as coming from Tibet and Mongolia are revealed to be most probably Cu-diffusion treated