Wenlanzhangite–(Y) from the Yushui deposit, South China: a potential proxy for tracing the redox state of ore formation

Abstract

Abstract Mineral phases in which vanadium (V) and heavy–rare–earth elements (HREEs) coexist are rarely documented. Here, we report a new V–HREE–bearing silicate mineral species, wenlanzhangite–(Y), which is a vanadiferous derivate of jingwenite–(Y) [Y2Al2V4+2(SiO4)2O4(OH)4] coexisting with jingwenite–(Y) in bedded/massive ores at Yushui, South China. Wenlanzhangite–(Y) forms as a dark brown, 70–100 μm–thick rim on a core domain of jingwenite–(Y), which occurs as 100–200 μm columnar crystals. The colour, streak, lustre, and hardness (Mohs) are dark brown, yellow grey, vitreous, and ~4, respectively. Compared to jingwenite–(Y), wenlanzhangite–(Y) has higher vanadium and lower aluminium contents. Calculated on the basis of 8 cations, the empirical formula is (Y1.26Dy0.17Er0.11Gd0.09Yb0.09Nd0.09Sm0.06Sc0.04Ho0.03Ce0.02Tb0.02Tm0.02Pr0.01)Σ2.00(V3+1.46Al0.54)Σ2.00V4+2(SiO4)2O4(OH)4, which can be simplified to the ideal formula Y2V3+2V4+2(SiO4)2O4(OH)4. Wenlanzhangite–(Y) is triclinic, with space group P–1(#2), Z = 2, and unit–cell parameters a = 5.9632(7) Å, b = 9.599(1) Å, c = 9.9170(9) Å, α = 90.033(8)°, β = 98.595(2)°, γ = 90.003(9)°, and V = 561.28(10) Å3. Wenlanzhangite–(Y) is approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2022–142). The structure of wenlanzhangite–(Y) is composed of a–axis–oriented chains of [VO6] octahedra consisting of edge–sharing octahedra linked by insular [SiO4] tetrahedra, leaving open channels occupied by rare earth elements. Observed compositional variation and crystal structure demonstrate that V3+ can substitute for Al3+ in jingwenite–(Y), forming wenlanzhangite–(Y). The occurrence of wenlanzhangite–(Y) indicates a relatively more reducing hydrothermal environment causing reduction of V5+ in oxidized fluids to V3+ and thus represents a useful proxy for tracing the redox state of ore formation.