Zhonghongite, Cu29 (As, Sb)12S33, a new mineral from the high-sulfidation vein of Jiama porphyry system, Tibet, China

Abstract Zhonghongite (IMA2023-046), ideally Cu29(As, Sb)12S33, is a new mineral discovered in the high-sulfidation vein of the Jiama deposit (E 91°45′, N 29°42′), southern Tibet, China. It forms complex intergrowths with watanabeite and tennantite-tetrahedrite, creating veined or massive aggregates ranging from millimeters to centimeters in size. The single crystals of zhonghongite are anhedral grains, with sizes ranging from several micrometers to approximately 100 micrometers. The mineral is gray in color with a black streak and metallic luster. It is brittle, with uneven fractures, and has a calculated density of 4.925g/cm3. The average values of electron microprobe analyses (wt.%) are as follow: Cu 42.19, As 11.11, Sb 16.09, S 25.45, Hg 3.73, Mn 0.67, and Te 0.28. The empirical formula, based on 33 sulfur apfu, is (Cu27.60Hg0.77Mn0.51Fe0.07Ag0.02)Σ28.97(As6.16Sb5.49Te0.09)Σ11.74S33. In zhonghongite, the substitution of Sb for As is limited, with the atomic ratio of As/(As+Sb) ranging from 0.457 to 0.629. Hg, Mn, and Fe, together with minor Cu, are divalent and serve for charge balance. Zhonghongite is orthorhombic, space group F2mm (42), a = 10.37741(5) Å, b = 14.69821(9) Å, c = 36.7645(2) Å and V = 5607.66(5) Å3. The crystal structure has been solved and refined by single-crystal X-ray diffraction with a final R1 = 0.0235 for 27028 (2467 unique) reflections. It is composed of individual AsS3 tripyramids and clustered tripyramids As4S7, CuS4 tetrahedra and CuS3 planar triangles, connected through corner S atoms in tetrahedral coordination and octahedral coordination with Cu and/or As. The structure is a derivative of tetrahedrite-type structure. Zhonghongite was formed under high-temperature conditions and is classified as an intermediate-sulfidation state mineral.