Alluvial gem sapphires from the Denchai area, northern Thailand, have O-isotope compositions ranging from +4.7‰ to +6.1‰ (15 samples), with one outlier, +8.4‰. It is suggested that these sapphires are not in O-isotope equilibrium with and must be xenocrysts from the nearby alkali basalts, which contain olivine phenocrysts with δ18O = +4.9‰ to +5.1‰ and are the presumed sources of these gem sapphires. Homogeneous δ18O values within individual sapphire crystal indicate limited interactions with the carrier magmas during transport to the surface. The O-isotope compositions of these sapphires suggest that crustal rocks might have been involved in the genesis of those sapphires with δ18O values higher than +5.5‰. A hybrid origin model for the Denchai sapphires is, therefore, postulated, which involves different degrees of interactions between a fractionated partial melt from (metasomatized) mantle and a lower/mid-crust Al-rich rock. © 2002 Elsevier Science B.V. All rights reserved.

Item Type:	Refereed Article
Research Division:	Earth Sciences
Research Group:	Geology
Research Field:	Igneous and Metamorphic Petrology
Objective Division:	Mineral Resources (excl. Energy Resources)
Objective Group:	Other Mineral Resources (excl. Energy Resources)
Objective Field:	Mineral Resources (excl. Energy Resources) not elsewhere classified
Author:	Zaw, K (Professor Khin Zaw)
Author:	Limtrakun, P (Mr Phisit Limtrakun)
ID Code:	28049
Year Published:	2003
Web of Science® Times Cited:	22
Deposited By:	Centre for Ore Deposit Research - CODES CoE
Deposited On:	2003-08-01
Last Modified:	2004-03-19
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