In Situ U-Th-Pb Dating of Parisite: Implication for the Age of Mineralization of Colombian Emeralds

Parisite-Ce (Ca(Ce,La)(2)(CO3)(3)F-2) is a rare-earth (REE) fluorocarbonate mineral first described from the world-famous emerald mines of the Muzo district, Boyaca Province, Colombia. Four samples of parisite-Ce collected from outcrops near Muzo have been geochemically studied and dated using the in situ laser ablation U-Th-Pb method. Our study shows that the REE abundance of parisite is controlled by the leaching of the wall rocks (black schist). Furthermore, we show that the parisite-Ce crystals formed in textural equilibrium with the emeralds, suggesting a similar time of crystallization. Our analysis demonstrates the capability of parisite as a geochronometer and shows that precise and accurate U-Th-Pb ages can be obtained from parisite after common Pb-207 correction. A higher precision date was obtained with the Th-Pb ratio rather than with the U-Pb ratio because of the relatively higher content of Th than U in the samples. The samples yielded Th-208-Pb-232 ages ranging from similar to 47 to 51 Ma. The new ages are similar to 10 Ma older than previously reported Ar-Ar ages and similar to 10 Ma younger than previously reported Rb/Sr ages. These results will have significant implications for understanding the timing of mineralization and crystallization of emerald deposits in Colombia. Furthermore, this study opens new avenues for dating similar deposits worldwide.