Ruizhongite, (Ag2☐)Pb3Ge2S8, a thiogermanate mineral from the Wusihe Pb-Zn deposit, Sichuan Province, Southwest China

Abstract

Abstract Ruizhongite (IMA2022-066), (Ag2☐)Pb3Ge2S8, is a thiogermanate of economic importance discovered in the Wusihe Pb-Zn deposit in Sichuan Province, southwestern China. This mineral occurs as anhedral grains 1–10 μm in size. It is gray and opaque, with a metallic luster and black streak, closely associated with galena and pyrite in a sphalerite matrix. Under reflected light, it displays a greenish-gray color without internal reflection. Its reflectance values in air (R %) based on SiC as the reference material are 30.5, 32.2, 34, and 34.1 for corresponding wavelengths of 650, 589, 470, and 546 nm, respectively. According to the average of 18 electron microprobe analyses, Pb (57.37 wt%), S (21.39 wt%), Ge (11.53 wt%), Ag (7.34 wt%), Zn (1.57 wt%), and Fe (0.27 wt%) constitute 99.46 wt% of ruizhongite. The empirical formula based on the 8 S apfu is (Ag0.82Pb0.32Zn0.28Fe0.06)Σ1.48Pb3Ge1.9S8, and (Ag2☐)Pb3Ge2S8 is its ideal formula. Ruizhongite displays a cubic structure, space group I43d (#220), with the unit-cell parameters a = 14.0559(2), V = 2777.00(7), Z = 8, and the calculated density is 5.706 g/cm3. The strongest powder X-ray diffraction lines [d in Å (I) (hkl)] are 3.755 (100) (123), 3.511 (76) (004), 2.992 (73) (233), 2.574 (21) (125), 2.482 (79) (044), 2.276 (46) (235), 1.784 (39) (237), and 2.075 (24) (136). The structure of ruizhongite was determined using single-crystal XRD and was refined to an R1 of 0.0323 for all 2594 (474 unique) reflections. The structure comprises a non-centrosymmetric arrangement of [GeS4]4− tetrahedra, forming two interstice sites: fully occupied Pb1 and partially occupied Ag1, aligned in the directions of a-, b-, and c-axes. Ruizhongite was named in honor of Ruizhong Hu (1958), an eminent Chinese ore geochemist. The discovery of ruizhongite has significant implications for the occurrence and enrichment mechanism of Ge in sphalerite and other metallic minerals.