Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Exotic rocks and REE apatite mineralization of Ulugei Khid massif in the Mongolia
Abstract
The exotic rock suite of Ulugei Khid Massif is genetically related to alkaline magmatism of the Northern Gobi rift zone (Main Mongolia lineament) in South Mongolia. The most exotic carbonatites and nelsonites are coarse-grained rocks, consisting mainly of primary calcite, apatite and magnetite, followed by flogopite, REE-fluoro-carbonates, barite, celestine and other rare accessories. Apatite is the most important mineral phase of nelsonites and the second most abundant mineral in carbonatites studied. Representative crystals of apatite exhibit magmatic zoning when the measured LREE contents slowly decrease from the core towards the rim in all analyzed objects. General geochemical features of examined carbonatites and nelsonites are characterized by low concentrations of Nb, Ta, Th and U, and by very high contents of P, LREE, Ba, Sr, with extremely high positive Eu anomaly that is contrary to the associated silicate rocks and generally to any other carbonatite or nelsonite in Mongolia. This confirms the hypotheses that the Ulugei Khid carbonatites and nelsonites originated during a very unusual magmatic event.
