Fleetite, Cu₂RhIrSb₂, a New Species of Platinum-Group Mineral from the Miass Placer Zone, Southern Urals, Russia

Journal Article · Tue Jun 08 00:00:00 EDT 2021 · Canadian Mineralogist

DOI:https://doi.org/10.3749/canmin.2000073· OSTI ID:1820121

Barkov, Andrei Y. ^[1]; Bindi, Luca ^[2]; Tamura, Nobumichi ^[3]; Martin, Robert F. ^[4]; Ma, Chi ^[5]; Winkler, Björn ^[6]; Shvedov, Gennadiy I. ^[7]; Morgenroth, Wolfgang ^[8]

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1. Cherepovets State University, Cherepovets (Russian Federation). Research Laboratory of Industrial and Ore Mineralogy
2. Università degli Studi di Firenze (Italy). Dipartimento di Scienze della Terra
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
4. McGill Univ., Montreal, QC (Canada). Dept. of Earth and Planetary Sciences
5. California Institute of Technology (CalTech), Pasadena, CA (United States). Division of Geological and Planetary Sciences
6. Universität Frankfurt, Frankfurt (Germany). Institut für Geowissenschaften
7. Siberian Federal Univ., Krasnoyarsk (Russian Federation). Institute of Mining, Geology and Geotechnology
8. Universität Potsdam, Potsdam-Golm (Germany). Institut für Geowissenschaften

Fleetite, Cu₂RhIrSb₂, a new species of platinum-group mineral (PGM), was discovered intergrown with an Os–Ir–Ru alloy in the Miass Placer Zone (Au–PGE), southern Urals, Russia. A single grain 50 μm across was found. Osmium, ruthenium, and iridium are the main associated minerals; also present are Pt–Fe alloys, laurite, Sb-rich irarsite, Rh-rich tolovkite, kashinite, anduoite, ferronickelplatinum, heazlewoodite, PGE-bearing pentlandite and digenite, as well as micrometric inclusions of forsterite (Fo_93.7), chromite–magnesiochromite, and Mg-rich edenite. In reflected light, fleetite is light gray; it is opaque, isotropic, non-pleochroic, and non-bireflectant. We report reflectance values measured in air. A mean of seven point-analyses (wavelength-dispersive spectrometry) gave Cu 13.93, Ni 8.60, Fe 0.10, Ir 28.07, Rh 7.91, Ru 1.96, Sb 39.28, total 99.85 wt.%, corresponding to (Cu_1.41Ni_0.58Fe_0.01)_Σ2.00(Rh_0.49Ni_0.36Ru_0.12)_Σ0.97Ir_0.95Sb_2.08 on the basis of six atoms per formula unit, taking into account the structural results. The calculated density is 10.83 g/cm³. Single-crystal X-ray studies show that fleetite is cubic, space group Fdm (#227), a = 11.6682(8) Å, V = 1588.59(19) ų, and Z = 16. A least-squares refinement of X-ray powder-diffraction data gave a = 11.6575(5) Å and V = 1584.22(19) ų. The strongest five reflections in the powder pattern [d in Å(I)(hkl)] are: 6.70(75)(111), 4.13(100)(220), 3.52(30)(311), 2.380(50)(422), 2.064(40)(440). Results of synchrotron micro-Laue diffraction experiments are consistent [a = 11.66(2) Å]. The crystal structure of fleetite was solved and refined to R = 0.0340 based upon 153 reflections with F_o > 4σ(F_o). It is isotypic with Pd₁₁Bi₂Se₂ and best described as intermetallic, with all metal atoms in 12-fold coordination. Fleetite and other late exotic phases were formed by reaction of the associated alloy phases with a fluid phase enriched in Sb, As, and S in circulation in the cooling ophiolite source-rock. The mineral is named after Michael E. Fleet (1938–2017) in recognition of his significant contributions to the Earth Sciences.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); Russian Foundation for Basic Research
• Grant/Contract Number: AC02-05CH11231; RFBR-19-05-00181
• OSTI ID: 1820121
• Journal Information: Canadian Mineralogist, Vol. 59, Issue 2; ISSN 0008-4476
• Publisher: Mineralogical Association of Canada
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
fleetite
Cu2RhIrSb2
new mineral species
platinum-group elements
ore minerals
platinum-group minerals
ophiolites
placer deposits
Miass placer zone
southern Urals
Russia