Magmatic platinum nanoparticles in metasomatic silicate glasses and sulfides from Patagonian mantle xenoliths

• Published in: Contributions to mineralogy and petrology 2019-05, Vol.174 (5), p.1-18, Article 47
• Main Authors: González-Jiménez, José María, Roqué-Rosell, Josep, Jiménez-Franco, Abigail, Tassara, Santiago, Nieto, Fernando, Gervilla, Fernando, Baurier, Sandra, Proenza, Joaquín A., Saunders, Edward, Deditius, Artur P., Schilling, Manuel, Corgne, Alexandre
• Format: Article
• Language: English
• Subjects: Alloys; Arsenic compounds; Arsenides; Basalt; Criminal investigation; Crystallization; Earth and Environmental Science; Earth Sciences; Electron microscopy; Fayalite; Fractionation; Fugacity; Geology; Heavy metals; High temperature; Ilmenite; Ion beams; Iron oxides; Magma; Magnetite; Mantle; Mantle (Geology); Melts; Metal sulfides; Metals (Materials); Microscopy; Mineral Resources; Mineralogy; Nanoparticles; Nickel ores; Noble metals; Original Paper; Oxides; Pentlandite; Peridotite; Petrology; Platinum; Precious metals; Precipitation (Meteorology); Saturation; Silicates; Silicon compounds; Specialty metals industry; Spinel; Spinel group; Sulfides; Sulfur; Sulfur compounds; Sulphides; Sulphur; Temperature; Transmission electron microscopy; Xenoliths
• ISSN: 0010-7999; 1432-0967
• DOI: 10.1007/s00410-019-1583-5

Platinum-rich nanonuggets ( s.l., nanoparticles) are commonly produced in experiments attempting to quantify the solubility or partitioning of noble metals in silicate and sulfide melts. However, it has been thought that these represent artifacts produced during quenching of the experimental runs. Here, we document nanoparticles (~ 20–80 nm) of Pt-rich alloys and arsenides dispersed in high-temperature metasomatic silicate glasses and in base-metal sulfides (BMS) entrained in them, found interstitially between minerals of mantle peridotite xenoliths from southern Patagonia. Pt-rich nanoparticles found in the interstitial silicate glasses are frequently attached to, or in the proximities of, oxides (ilmenite or Cr-spinel) suggesting a close link between the formation of the oxides and the Pt-rich nanoparticles. The interstitial glasses in the studied xenoliths correspond to quenched alkaline basaltic melts that infiltrated the subcontinental lithospheric mantle (SCLM) at > 1000 °C at an oxygen fugacity ( f O 2 ) near the fayalite–magnetite–quartz (FMQ) buffer. Experimental works indicate that at these conditions the crystallization of oxides such as ilmenite or Cr-spinel may lower f O 2 to promote the precipitation of Pt-rich nanoparticles. The investigation of four Pt-rich nanoparticles hosted in two different pentlandite grains using a combination of focused ion beam and high-resolution transmission electron microscopy (FIB/HRTEM) show that these nanoparticles consists of polycrystalline aggregates