Sapphire within zircon-rich gem deposits, Bo Loei, Ratanakiri Province, Cambodia: trace elements, inclusions, U-Pb dating and genesis
Sutherland, FL and Piilonen, PC and Zaw, K and Meffre, S and Thompson, J, Sapphire within zircon-rich gem deposits, Bo Loei, Ratanakiri Province, Cambodia: trace elements, inclusions, U-Pb dating and genesis, Australian Journal of Earth Sciences, 62, (6) pp. 761-773. ISSN 0812-0099 (2015) [Refereed Article]
Crown Copyright in the Commonwealth of Australia 2015 Australian Museum
Subordinate sapphire accompanies prevalent zircon megacrysts in the Bo Loei basaltic gem field, Ratanakiri Province, Cambodia. These deposits are important for heat-treated gem zircon. Dark blue sapphire, with rare blue-green, orange-brown and yellow stones, up to a few cm in size, include hexagonal-shaped and growth-zoned crystals. Analyses of the sapphires (electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry) showed Fe as the main chromophore (0.62.7 wt%), with minor Ti (<0.7 wt%). Sapphire cores show enrichment in Fe relative to rims and some include exotic heavy elements (Nb up to 56, Ta up to 144, Sn up to 5 ppm). The sapphires show high Ga values (271724 ppm) and Ga/Mg ratios (4.877.0) suggesting magmatic associations. Two sapphires with syngenetic inclusions (zircon, Nb-rich rutile) gave UPb (Th-disequilibrium corrected) ages at ca 0.93 ± 0.1 Ma. The Bo Loei sapphires show higher Fe and Ga than other magmatic sapphire suites elsewhere in Cambodia (Pailin), Laos (Ban Huai Sai, Ban Sam Sai), South Vietnam (Dak Nong, Dak Lac) and SE Thailand (Chanthaburi-Trat). This suggests potential for geographic typing of sapphire suites between these different fields.