Hydrothermal transformations of triphylite from the Nanping No. 31 pegmatite dyke, southeastern China
Rao, Can; Wang, Ru Cheng; Hatert, Frédéric; Baijot, Maxime
European Journal of Mineralogy Volume 26 Number 1 (2014), p. 179 - 188
published: Feb 1, 2014
Open Access (paper can be downloaded for free)
The mineralogy of triphylite and associated phosphates was investigated in the Nanping No. 31 pegmatite, southeastern China. Two types of triphylite were distinguished, based on their petrological features and chemical compositions. Triphylite-I occurs as small granular aggregates in fine grained white mica from zones III and IV, whereas triphylite-II occurs as veinlets or aggregates in the fractures and/or on the rims of primary montebrasite from zone IV. Various hydrothermal transformations were observed in both types of triphylite. Triphylite-I successively transformed to lazulite, wagnerite, fluorarrojadite-(BaNa) and fluorapatite, suggesting successive replacement processes during Mg-rich, Na-rich, and Ca-rich hydrothermal stages. Triphylite-II is mainly replaced by fluorapatite, anapaite, and ludlamite; these replacement processes result from cationic exchanges in combination with hydration, due to the presence of Ca-bearing fluids.