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GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 282-9
Presentation Time: 3:50 PM

GEOGRAPHIC ORIGIN DETERMINATION OF RUBY AND SAPPHIRE USING SR - PB ISOTOPES


KREBS, Mandy Y.1, PEARSON, D. Graham2, FAGAN, Andrew J.3 and SARKAR, Chiranjeeb2, (1)GEMOLOGICAL INSTITUTE OF AMERICA, 50 W 47th St, New York, NY 10036, (2)Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada, (3)Hummingbird Geological Services, Vancouver, BC V6B 1L8, Canada

The geographic origin of gemstones has emerged as one of the main factors affecting their sale on the international market, in large part due to the prestige attributed to certain origins but also because of political and ethical reasons. This provides a strong motivation to establish accurate scientific methods to identify the provenance of top of the line colored stones such as ruby and sapphire.

Analytical methods currently used to determine gem corundum provenance (observation of inclusions and gemological features, trace element analysis) have proven useful in distinguishing rubies and sapphires from different geological settings but are not yet able to reliably distinguish between gems from different geographic regions that share a similar geological setting. The lack of a unique fingerprint emphasizes the need for a more powerful tool for geographic origin determination, especially for high-clarity stones.

Using a novel offline laser ablation technique followed by thermal ionization mass spectrometry (TIMS) we were able to precisely measure radiogenic isotope compositions in gem corundum for the first time, demonstrating, on the basis of rubies from three different localities and two different deposit types, that radiogenic isotopes potentially offer a powerful means of provenance discrimination even for geologically similar deposits.

Here we present Sr and Pb isotope data for rubies and sapphires from several different localities of geologically similar deposits; Rubies from amphibole-related (Mozambique, Tanzania, Madagascar, Greenland), marble-related (Vietnam, Myanmar, Tanzania, Afghanistan), and basalt-related deposits (Thailand, Cambodia), and metamorphic blue sapphires (Myanmar, Sri Lanka, Madagascar). This data will be evaluated with regard to its usefulness in determining the geographic origin of both ruby and sapphire and the method’s usefulness for the development of a unique fingerprint for the country of origin determination will be discussed.

Session No. 282

T113. Gemological Research in the Twenty-First Century—Characterization, Exploration, and Geological Significance of Diamonds and Other Gem Minerals
Wednesday, 7 November 2018: 1:30 PM-5:30 PM
Room 145 (Indiana Convention Center)
Geological Society of America Abstracts with Programs. Vol. 50, No. 6
doi: 10.1130/abs/2018AM-321398
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