Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Arfvedsonite pegmatites of Khan Bogd massif, Mongolia: Zr mineralization
Abstract
The alkaline granitic massif Khan Bogd is located in the Gobi desert in southern Mongolia. The Khan Bogd, one of the world's largest alkaline ring complexes, is a product of strong fractional crystallization. Detailed field and petrographical research indicates that the aplite-pegmatite emplacement occurred during transitions from the ductile to the brittle regime from the most evolved granitic melt. This paper is focused mainly on the arfvedsonite pegmatites. The mineral paragenesis of the selected pegmatites is dominantly formed by quartz, elpidite, K-feldspar, albite, aegirine and arfvedsonite. Among widespread accessories the unidentified hydrated Zr-REE silicates, armstrongite and zirkon are the most considerable. The key enrichment in Zr and REE is related to magmatic process, but the alteration and metasomatism (replacement of primary elpidite mainly by secondary zircon and armstrongite) in pegmatites play also important role.
