The geochemistry and mineralogy of zircons from Sri Lanka

RUPAS1NGHE, M. S. and DISSANAYAKE, C. B., 1987: The geochemistry and mineralogy of zircons f rom Sri Lanka. Bull. Geo!. Soc. Finland 59, Part 1, 3—19. A total of 51 sediment samples and 40 rock samples f rom the main gem fields of Sri Lanka have been analysed for their Zr contents. The results indicated a marked enrichment of Zr in the sediments as against the probable source rocks. Fortynine zircon separates from the gem-bearing sediments were analysed by electron microprobe and neutron activation for their trace and rare-earth element concentrations. Of the green, yellow, violet and rose zircon varieties studied, the green zircons showed relatively high enrichment in Th, U and Hf. Chondrite-normalized REE plots for five zircon separates revealed markedly similar patterns with H REE enrichments. The similarity of the plots could well indicate a similar source of origin for the zircons. Seven zoned zircons were also studied for their elemental composition. Even though there were periodic changes in the elemental composition within one zone, there were, on an average, no distinct elemental variations from the rim to the core of the zircon grain.