The Avdar intrusion is an amazonite-bearing Li- and F-rich leucogranite stock in central Mongolia. This Late Triassic dome-shaped intrusion is about 6 km long and 2–2.5 km wide and intruded into the Devonian clastic strata. The intrusion is a composite body, with a core of medium-grained leucogranite surrounded by amazonite leucogranite. Both LiF granites are composed of albite, quartz, K-feldspar, minor Li-bearing biotite (annite), and fluorite. Common accessory minerals include metamictic zircon, FeTi oxides, cassiterite, and columbite-tantalite. The rocks are peraluminous A-type (anorogenic) granites high in silica, alumina, and alkalis but low in CaO. They are highly enriched in F, Li, Rb, Cs, Ta, Nb, and Sn and depleted in Ba, Sr, Eu, Ti, and P. The ɛNd(t) values are relatively uniform, overlapping for both phases (+1.1 to +1.4). Their chondrite-normalized REE patterns show the “tetrad effect” accompanied by a strong negative Eu anomaly. The rocks also have very low Zr/Hf (<15) and Na/Tb (<5) ratios characteristic of fluorine-mediated fractionation. The pluton was emplaced in a post-orogenic extensional setting, where upwelling of asthenospheric mantle provided the heat to trigger partial melting of juvenile, dehydrated continental crust, while regional extension allowed highly differentiated magmas to rise into the upper crust. Fluids likely contributed trace elements (e.g., Li, F, Rb) to the magmatic system, enhancing the potential for rare-metal mineralization. Geochemical characteristics indicate that the Li-F-rich granites could host mineralization of Sn, Li, Ta and Nb.
