Abstract
ABSTRACTStibiogoldfieldite, Cu12(Sb2Te2)S13, was approved as a new mineral species from the Mohawk mine, Goldfield mining district, Esmeralda County, Nevada, USA. It occurs as metallic anhedral grains, dark grey in colour. It is associated with quartz, pyrite and an Ag–Bi–(S,Se) phase (holotype material) and with quartz, pyrite, calaverite, bismuthinite, bohdanowiczite, and the Ag–Bi–(S,Se) phase (cotype material). In reflected light, stibiogoldfieldite is isotropic, grey in colour, with indistinct brownish shade. Reflectance data in air [R (%)] are: 31.1 at 470 nm, 30.9 at 546 nm, 30.8 at 589 nm and 31.0 at 650 nm. Electron microprobe analysis for holotype material gave (in wt.% – average of 60 spot analyses): Cu 45.03(60), Ag 0.26(7), Fe 0.02(3), Zn 0.13(15), Sn 0.02(4), Pb 0.05(6), Sb 8.02(62), As 2.80(65), Bi 2.77(87), Te 15.15(1.24), S 24.50(32), Se 0.52(11), total 99.27(69). On the basis of (As + Sb + Te + Bi) = 4 atoms per formula unit (apfu), the empirical formula of stibiogoldfieldite is (Cu12.05Ag0.04Zn0.03Fe0.01)Σ12.13(Sb1.12As0.63Bi0.23Te2.02)Σ4.00(S12.99Se0.11)Σ13.10. Chemical data on an additional sample from the same locality (cotype material) gave the following results (in wt.% – average of 181 spot analyses): Cu 43.84(63), Ag 0.21(7), Sb 5.92(78), As 2.63(45), Te 20.07(1.19), S 25.13(53), Se 0.97(35), total 99.47(66). On the basis of (As + Sb + Te + Bi) = 4 apfu, the empirical formula of cotype material is (Cu11.30Ag0.03)Σ11.33(Sb0.80As0.57Bi0.06Te2.57)Σ4.00(S12.83Se0.20)Σ13.03. Stibiogoldfieldite is cubic, I$\overline 4$3m, with unit-cell parameters a = 10.3466(17) Å, V = 1107.6(5) Å3 and Z = 2 (holotype). Unit-cell parameters for the cotype sample are a = 10.3035(2) Å and V = 1093.83(7) Å3. The crystal structure of holotype stibiogoldfieldite was refined by single-crystal X-ray diffraction data to a final R1 = 0.032 on the basis of 285 reflections with Fo > 4σ(Fo) and 20 refined parameters. Stibiogoldfieldite is isotypic with other members of the tetrahedrite group.
Highlights
The tetrahedrite group includes the most common sulfosalts occurring in hydrothermal ore deposits, where they host different elements owing to the possibility of several homo- and heterovalent substitutions (Moëlo et al, 2008; Biagioni et al, 2020)
This compositional diversity is reflected in the relatively large number of mineral species belonging to this group that have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA–CNMNC)
In addition to the 11 mineral species redefined in Biagioni et al (2020), a total of 32 potential end-member compositions has been hypothesised in the tetrahedrite group based on the literature
Summary
The tetrahedrite group includes the most common sulfosalts occurring in hydrothermal ore deposits, where they host different elements owing to the possibility of several homo- and heterovalent substitutions (Moëlo et al, 2008; Biagioni et al, 2020). Chemical data on an additional sample from the same locality (cotype material) gave the following results (in wt.% – average of 181 spot analyses): Cu 43.84(63), Ag 0.21(7), Sb 5.92(78), As 2.63(45), Te 20.07(1.19), S 25.13(53), Se 0.97(35), total 99.47(66).
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