关键词: 癞子岭, 云英岩, Li-F云母, 岩浆-热液作用

Abstract: The Laiziling granitic pluton comprises three rock phases with a pronounced vertical lithological zonation, granite, greisen
and pegmatite from base to top. Greisen from the Laiziling granitic pluton is characterized by its huge thickness, micas belonging to the
zinnwaldite, high abundance of topaz and high W-Sn-Nb-Ta concentration. Petrological, geochemical and mineralogical studies have
been carried out on the Laiziling greisen. It is concluded that the Laiziling greisen is a peraluminous rock with high silicon content, low
content of total alkali (3-4.3 wt%), Zr/Hf (~8) and Nb/Ta (~1.7) ratios, and enrichment of the volatiles. Micas in the Laiziling greisen
are classified into zinnwaldite, and LA-ICP-MS analysis results indicate they have high content of Nb (~74×10-6), Ta (~66×10-6), W
(~23×10-6) and Sn (~75×10-6) concentrations. Zircons in the Laiziling greisen are commonly euhedral and homogeneous and contain
high HfO2 (~10 wt%) content, and Zr/Hf ratio as low as 5. The compositions of zircon display a successive change compared with those
from the Laiziling albite granite. These chemical characteristics of the greisen are similar to those of highly fractionated rare-metal
granites and pegmatites in the Nanling Range with similar fractionation degree. Columbite-group minerals, cassiterite and wolframiteare found in the Laiziling greisen, suggesting the obvious W-Sn-Nb-Ta mineralization. Both mineral textures and chemical
compositions indicate these oxide minerals formed in the magmatic stage. Granitic magma contains high concentrations of volatiles (Li
and F), which play a very important role in the petrogenesis and the rare-metal mineralization of greisen. Li and F were incorporated
into the Li-F mica and topaz and rare metal mineralization formed in the late stage of magmatism enriched in large amount of fluid.
Consequently, greisen could probably be the product by the strong fractionation and fluid activity after the albite granite formed in the
same granitic chamber. The results should open a new window for understanding the petrogenesis and rare-metal mineralization in the
granitic magmatic-hydrothermal system.

Key words: Laiziliang, greisen, Li-F mica, magmatic-hydrothermal process