Age Determination of Zircon Inclusions in Faceted Sapphires

The age determination of zircon inclusions in faceted sapphires by LA-ICP-MS may provide a valuable tool to support geographical origin determination. In this initial study, U-Pb dating of a zircon inclusion in a pink sapphire from Madagascar yielded an age of 650 million years (Ma), suggesting a syngenetic origin (i.e. formed at the same time as the host sapphire) of the zircon. In a greenish blue sapphire from Madagascar, an included zircon yielded a U-Pb age of 1,750 Ma, pre-dating the host sapphire, and therefore indicating the zircon is an inherited inclusion (i.e. it originated from rocks that existed before the host sapphire crystallized). These results are supported by indications provided from conventional methods of geographical origin determination. This article also discusses the potential influence on U-Pb age dating of post-formation metamorphic events, laboratory heat treatment and the possibility of complex zoning in the zircon inclusions. (C) 2015 The Gemmological Association of Great Britain