Potential sources for alluvial gem corundum and zircon from the Rio Mayo area, near Mercaderes, Colombia are reviewed, based on U-Pb dating of syngenetic and protogenetic mineral inclusions in corundum samples and on a zircon megacryst. Corundum recovered from the region (approx. 99% sapphire, 1% ruby) commonly shows growth banding, includes colour change stones and exhibits overlaps in colour ranges and inclusion characteristics. This suggests a contiguous genetic suite. The U-Pb dating used laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) techniques. Because of the young ages and low-U contents of the dated zircons, the acquired data required a special statistical treatment. The results from zircon, fluorapatite and allanite-(Ce) inclusions provide a corundum crystallization age of 8 to 11Ma, in relation to northern Andean Miocene uplift and magmatism. The zircon megacryst gave a younger crystallization age of c. 0.6Ma, unrelated to the corundum genesis. Geochemical parameters (trace element and O isotope ranges) for corundum samples suggest a metamorphic/metasomatic origin. The age data rules out corundum genesis during the Late Cretaceous ophiolitic generation, but leave open possible later metasomatic interactions with this substrate. The Cr/Ga and Ga/Mg ratios and O isotope range for the corundum fall within the known limits for metasomatic, desilicated felsic/ultramafic 'plumasitic' associations, suggesting a possible parental source. Allanite, extremely rare as an inclusion in corundum elsewhere, may prove a characteristic inclusion for Rio Mayo corundum. © 2008 Elsevier B.V.

Item Type:	Refereed Article
Research Division:	Earth Sciences
Research Group:	Geology
Research Field:	Resource geoscience
Objective Division:	Mineral Resources (Excl. Energy Resources)
Objective Group:	Mineral exploration
Objective Field:	Titanium minerals, zircon, and rare earth metal ore (e.g. monazite) exploration
UTAS Author:	Meffre, SJM (Professor Sebastien Meffre)
ID Code:	56644
Year Published:	2008
Web of Science® Times Cited:	36
Deposited By:	Centre for Ore Deposit Research - CODES CoE
Deposited On:	2009-05-19
Last Modified:	2014-11-07
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