Wenqingite, Pb5(AsS3)2(Ge2S6), the first thiogermanate and thioarsenite mineral with edge-sharing GeS4 tetrahedra, from the Wusihe Pb–Zn deposit, Sichuan Province, SW China

Abstract Wenqingite (IMA2024-098), Pb5(AsS3)2(Ge2S6), is the first thiogermanate and thioarsenite mineral of considerable economic significance, discovered in the Wusihe Pb–Zn deposit in SW China. It is greenish gray with a metallic luster and black streak. Wenqingite occurs as euhedral to subhedral columnar or platy crystals with a grain size of 1–10 μm, and is closely associated with galena, pyrite, jordanite, and ruizhongite within a sphalerite matrix. Under reflected light microscopy, it displays a greenish gray color without internal reflection. Reflectance measurements in air, using SiC as a reference material, yield R1 (%) values of 26.1, 27.9, 29.1, and 30.5, and R2 (%) values of 24.2, 26.0, 27.2, and 27.5, corresponding to wavelengths of 650, 589, 546, and 470 nm, respectively. Wenqingite is composed of Pb (57.95 wt%), S (22.85 wt%), Ge (8.29 wt%), As (7.60 wt%), Sb (1.84 wt%), Zn (1.39 wt%), and Fe (0.44 wt%), and a total of 100.36 wt%. The empirical formula is (Pb4.71Zn0.36Fe0.13)Σ5.20(As1.71Sb0.26) Σ1.97Ge1.92S12, calculated on the basis of 12 sulfur atoms per formula unit. The ideal formula is Pb5(AsS3)2(Ge2S6). Wenqingite has a monoclinic structure, space group P21/c (#14), with the unit-cell parameters a = 17.8564(12) Å, b = 10.8990(5) Å, c = 10.9637(6) Å, β = 108.277(6)°, V = 2,026.1(2) Å3, Z = 4, and calculated density of 5.543 g/cm3. The most intensive X-ray diffraction (XRD) lines [d in Å (I) (hkl)] are: 3.941 (75) (3, 2, 0), 3.895(100) (1, 2, −2), 3.367 (36) (5, 0, 0), 3.181 (36) (−4, 2. 2), 2.818 (82) (2, 1, 3), 2.544 (73) (−6, 2, 2), and 2.450 (91) (2, 2, −4). The structure of wenqingite was determined by single-crystal XRD, and was refined to an R1 of 0.0779 for 2990 independent reflections (I > 2σI) with 196 parameters. Its structure is characterized by edge-sharing GeS4 tetrahedral dimers (Ge2S6) and isolated AsS3 pyramids connected by PbSn polyhedra (n = 7, 8, 9), arranged separately in two electrically balanced layers of Pb2Ge2S6 and Pb3(AsS3)2. This new mineral was named in honor of Prof. Wenqing Qin (b. 1969), a distinguished Chinese scientist renowned for his contributions to mineral processing and the recycling of secondary resources. The discovery of wenqingite, along with ruizhongite in the Wusihe deposit provides critical insights into the geochemical behavior and enrichment mechanisms of Ge within sphalerite, and enhances the understanding of the mineralogical controls on the distribution patterns of the critical element Ge in sulfide-dominated mineral deposits.