| Reference Type | Journal (article/letter/editorial) |
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| Title | New minerals auropolybasite, [Ag15AuSb2S11] and auropearceite, [Ag15AuAs2S11], and the implications for the formation of bonanza ores in epithermal systems |
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| Journal | American Mineralogist |
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| Authors | Mikuš, Tomáš | Author |
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| Vlasáč, Jozef | Author |
| Majzlan, Juraj | Author |
| Plášil, Jakub | Author |
| Sejkora, Jiří | Author |
| Števko, Martin | Author |
| Petříček, Václav | Author |
| Makovicky, Emil | Author |
| Year | 2025 (July) |
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| URL | |
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| DOI | doi:10.2138/am-2025-9806Search in ResearchGate |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 18666272 | Long-form Identifier | mindat:1:5:18666272:0 |
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| GUID | 0 |
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| Full Reference | Mikuš, Tomáš; Vlasáč, Jozef; Majzlan, Juraj; Plášil, Jakub; Sejkora, Jiří; Števko, Martin; Petříček, Václav; Makovicky, Emil (2025) New minerals auropolybasite, [Ag15AuSb2S11] and auropearceite, [Ag15AuAs2S11], and the implications for the formation of bonanza ores in epithermal systems. American Mineralogist. doi:10.2138/am-2025-9806 |
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| Plain Text | Mikuš, Tomáš; Vlasáč, Jozef; Majzlan, Juraj; Plášil, Jakub; Sejkora, Jiří; Števko, Martin; Petříček, Václav; Makovicky, Emil (2025) New minerals auropolybasite, [Ag15AuSb2S11] and auropearceite, [Ag15AuAs2S11], and the implications for the formation of bonanza ores in epithermal systems. American Mineralogist. doi:10.2138/am-2025-9806 |
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| In | Link this record to the correct parent record (if possible) |
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| Abstract/Notes | The new minerals auropolybasite, ideally Ag15AuSb2S11 and auropearceite, ideally Ag15AuAs2S11, were found at the Šibeničný vrch near Nová Baňa in Slovakia. They were found as anhedral grains up to 0.2 mm in size, usually rimmed by acanthite. Both new minerals are associated with acanthite, argentopolybasite, argentopearceite, pyrargyrite, proustite, stephanite, selenostephanite, rozhdestvenskayaite-(Zn), zvěstovite-(Zn), zvěstovite (Fe), naumannite, Au-Ag alloys, uytenbogaardtite, iodargyrite and bromargyrite. They are dark grey to black, opaque, with a black streak and metallic luster. The Mohs hardness is ∼3. They are brittle with no observable cleavage and with a conchoidal fracture. The calculated density is 6.622 g·cm−3 for auropolybasite and 6.606 g·cm−3 for auropearceite. In reflected light, auropolybasite and auropearceite are grey with a bluish tint with no observable bireflectance and very weak pleochroism. They show moderate anisotropy in crossed polars with weak greenish and green–blue tints. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the IMA are (Rmin/Rmax, %): 33.5/31.6 (470 nm), 32.9/31.1 (546 nm), 32.1/30.6 (589 nm) and 30.2/29.3 (650 nm) for auropolybasite and 30.6/29.8 (470 nm), 30.3/29.2 (546 nm), 29.7/28.7 (589 nm) and 28.1/27.4 (650 nm) for auropearceite. The empirical formula (based on 29 apfu) for auropolybasite is: Ag15.27Au0.84(Sb1.51As0.46)Σ1.97(S10.55Se0.30Cl0.06)Σ10.91, and for auropearceite is: Ag15.84Au0.88(As1.33Sb0.44)Σ1.76(S10.46Se0.05Te0.01)Σ10.52. The ideal end-member formula for auropolybasite is Ag15AuSb2S11 and Ag15AuAs2S11 for auropearceite. Their symmetry is trigonal, space group P321. Latice parameters for auropolybasite are: a = 15.1091(5) Å, c = 12.1518(5) Å, V = 2402.42(15) Å3, Z = 4 and for auropearceite: a = 14.995(3) Å, c = 12.115(2) Å, V = 2359.3(8) Å3, Z = 4. The crystal structure of auropolybasite confirmed that the atomic arrangement is isotypic to that of the other members of the polybasite group and it is isostructural with auropearceite. These minerals form in the waning stages of epithermal systems, from reduced, S-rich and low-salinity fluids that transport Au, Ag, Sb and As in the form of thiocomplexes. These fluids are unable to transport Cu, Pb, or Zn, thus explaining the chemical composition of these minerals and the entire mineral assemblage. |
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