U-Pb Ages of Zircon Inclusions in Sapphires from Ratnapura and Balangoda (Sri Lanka) and Implications for Geographic Origin

Abstract

Five sapphires from the secondary placer deposits of Ratnapura and Balangoda in Sri Lanka were classified as being of metamorphic/metasomatic/non-basalt-related origin based on trace-element analysis (LA-ICP-MS) and inclusion characterization. Two sapphires—one from each deposit—contained suitable zircon inclusions that were dated using the LA-ICP-MS method. They yielded U-Pb ages of approximately 549 Ma. The results suggest that the zircon enclosed in the sapphires probably formed in a high-temperature event at the end of the Precambrian granulite facies metamorphism of the ancient Gondwana continent and that this event coincides with the crystallization of the sapphires. The metamorphic character of these sapphires is confirmed from the traceelement composition as well as the solid- and liquid-phase inclusions.