Discovery of xenotime-(Yb) and its geological significance in the north Wuyi area, Southeast China

Abstract

Xenotime-(Yb), a rare phosphate mineral enriched in HREEs, has not been previously reported in China. Based on field investigations and comprehensive petrographic and mineralogical analyses, including optical microscopy, laser Raman spectroscopy, SEM, EPMA, and LA-ICP-MS, xenotime-(Yb) is identified for the first time in quartz-wolframite veins of the Gexianshan granite, located in the North Wuyi area, Jiangxi Province, China. Xenotime-(Yb) occurs as discrete microscale particles (1–10 μm), either enclosed within wolframite or situated in its fissures. Within the isomorphic YbPO₄ –YPO₄ series, Yb/Y atomic ratios range from 0.08 to 1.50, producing distinct gray bands in BSE images. The RE₂O₃ content ranges from 67.1 % to 72.8 % and is dominated by HREEs, particularly Yb and Y. The apfu of Yb in xenotime-(Yb) vary significantly, from 0 to 0.4. Lu and Tm exhibit a positive linear correlation with Yb, while Y and Gd show a negative linear correlation. The compositional characteristics indicate complete isomorphic substitution among Lu, Tm, Y, Ga, and Yb, whereas Dy, Ho, Er, and Yb undergo incomplete substitution. The chemical formula of the Yb-rich end-member particle is (Yb_0.37Y_0.25Lu_0.16Er_0.12Dy_0.09Tm_0.03Ho_0.02Gd_0.01)_∑1.04P_0.97O₄. Raman spectroscopy reveals characteristic peaks for xenotime-(Yb), distinguishing it from xenotime-(Y) by a unique peak at 290 cm⁻¹. The discovery not only represents the first identification of xenotime-(Yb) in Jiangxi Province but also has important implications for the exploration of HREE resources and supports the potential application of YbPO₄ in materials science.