Abstract: Xiekusite pegmatite, a typical Li-Cs-Ta(LCT) pegmatite, is located in the Koktokay county of Altay, Xinjiang, and hosts a
large amounts of lithium minerals of phosphate and silicate. In this paper, in combination with field observations, the mineralogical
behavior of Li from the Xiekusite pegmatite has been studied for crystallization evolution and hydrothermal alteration of Li minerals
during magmatic to hydrothermal stages by electron micro-probe and X-ray diffraction analyses. The results show that (1) Li minerals
from the Xiekusite pegmatite crystallized through two stages, spodumene, montebrasite and lithiophylite formed during the magmatic
stage; while elbaite, polylithionite and trilithionite crystallized from the magmatic-hydrothermal transition stage to hydrothermal stage.
(2) The rock-inclusions of montebrasite-lithiophylite association reflect an immiscibility mechanism between Li phosphate melt and Li
silicate melt in the Xiekusite pegmatite. (3) Lithiophyllite was altered to a series of minerals which have similar structures but different
colors (from light yellowish to deep red ), suggestive of the oxidation and Li-leaching processes of lithiophyllite. (4) Li was leached into
fluids by hydrothermal alteration of Li minerals such as spodumene, montebrasite and lithiophylite, and secondary Li-bearing minerals
crystallized from the Li-rich fluids, these processes reflect the geochemical cycle of Li in the Xiekusite pegmatite.

Key words: lithium minerals, geochemical cycle of lithium, mineralogical behavior, pegmatite, Altay