• journal_title：The Canadian Mineralogist
• Contributor：Ru Cheng Wang ; Huan Hu ; Ai Cheng Zhang ; Xiao Long Huang ; Pei Ni
• Publisher：Mineralogical Association of Canada
• Date：2004-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.42.3.883
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：42
• issue：3
• firstpage：883
• section：Articles

The Yichun topaz–lepidolite granite is the youngest and most evolved unit of the Yichun granitic complex, southern China, and is well known by virtue of the unusual development of Ta–Nb–Li mineralization and enrichment in cesium in a granite. Three petrographic zones are recognized from the bottom upward: K-feldspar-rich facies, albite-rich facies, and albite- and K-feldspar-rich facies. The Cs contents increase with fractional crystallization of the magma, and reach a maximum in the middle part of the albite-rich facies (1709 ppm). Two principal carriers of Cs are observed in this facies: pollucite and the Cs-dominant analogue of polylithionite. In the middle part of this facies, both minerals occur as small inclusions within quartz or K-feldspar phenocrysts, indicative of a magmatic origin. However, in the upper part of this facies, pollucite appears interstitially among tabular crystals of albite around K-feldspar phenocrysts, suggesting that this type of pollucite postdates the rock-forming minerals, but formed prior to complete crystallization of the silicate melt. In addition, Cs-rich replacement zones typify the rim of lepidolite flakes in the groundmass. Lepidolite may contain up to 25.8 wt% Cs₂O, or ~ 0.9 Cs apfu (based on O = 11). Such lepidolite may be considered a Cs-dominant analogue of polylithionite. According to their distribution and compositional characteristics, pollucite and the Cs-dominant analogue of polylithionite seem to have formed at the late-magmatic or magmatic to hydrothermal transition stage of evolution of the leucogranitic magma at Yichun.