Tracing the emerald origin by oxygen isotope data: the case of Sandawana,Zimbabwe

Given the wide range of oxygen isotopic composition of emerald from all over the world (δ¹⁸O between +6.2 and +24.7‰), the δ¹⁸O_V-SMOW values of emeralds from the Sandawana mines in Zimbabwe (δ¹⁸O‰=+6.6 to +8.0), are relatively constant, among the lowest ever measured. These consistently low values can be explained by host-rock buffering in a very narrow emerald-bearing reaction zone between ultrabasic greenstones (metamorphosed komatiites) and albitised pegmatites. δ¹⁸O values of Sandawana emeralds overlap those of emeralds from Brazil, Austria, Australia and Madagascar, a fact indicating that, in these cases, oxygen isotope composition alone is not sufficient to determine the geographic origin of commercially available emeralds. However, stones with overlapping δ¹⁸O values may eventually be identified using a combination of physical properties, inclusion characteristics and chemical composition. To cite this article: J.C. Zwaan et al., C. R. Geoscience 336 (2004).