New data on PGE alloy minerals from a very old collection (probably 1890s), California
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Andrei Y. Barkov
und
Mark N. Feinglos
Abstract
We report results of multiple electron-microprobe analyses of nine grains of alloy minerals, 2-5 mm in size, rich in the platinum-group elements (PGE), from a unique, very old collection (~1890s) of placer material from Trinity Co., California. Osmium, iridium, ruthenium, and rutheniridosmine are the principal alloy species poor in Fe (typically <0.5-1 wt%); they appear to be primary. An Fe-enrichment (up to 4.6 wt%) is observed in lamellae of Ir-Ru-Os alloy exsolved from the Fe-poor Os-Ir-Ru alloy host, and also in a rim-like alteration-induced phase developed along the margin in some of the grains of Ir-Ru-Os alloy. Much greater levels of Fe (up to 19.1 wt%), incorporated via the substitution mechanisms: Fe → Ru, Fe → (Os + Ru), and Fe → Ir, were documented in three grains of Fe-Os-Ru-Ir alloys, which attain Fe-dominant compositions, i.e., hexaferrum. These Fe-Os-Ru-Ir alloys and associated exotic phases enriched in unconventional elements, such as W-(Mo)-bearing rutheniridosmine, (Os,Ir)5(W,Mo) and newly recognized (Ir,Os)5(W,Mo), appear to be secondary, formed under conditions of low fugacities of O2 and S2 as a result of interaction of primary Os-Ir-Ru alloys with a reducing fluid phase. No grains of Pt-Fe alloys were found; these only occur as Pt3Fetype (isoferroplatinum or Fe-rich platinum) and Pt2Fe-type inclusions (<50 μm), enclosed in a matrix of Ir- or Os-dominant alloys rich in Ru. The Pt2Fe alloy appears to be a compositional variant of Fe-rich platinum, possibly reflecting a lower limit of Pt content possible in the mineral platinum. An Au-Ag alloy, ranging up to Au0.99, precipitated pseudomorphously by a subsolidus reaction between a residual Au-Ag-rich melt and exsolution-induced inclusions of the Pt-Fe alloy phases. Micro-inclusions of olivine, hosted by a ternary alloy Os0.33Ru0.33Ir0.30, are extremely rich in Mg (Fo95.1-95.4), probably reflecting high-temperature reaction involving chromite or magnesiochromite. The alloy grains from the old collection were likely derived from a mineralized zone of ultramafic rocks, rich in chromitemagnesiochromite and poor in overall S, in the Trinity ophiolite complex of northern California.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Amorphous materials: Properties, structure, and durability: Atomic structure and transport properties of MgO-Al2O3 melts: A molecular dynamics simulation study
- Amorphous Materials: Properties, structure, and durability: Oxidation state of iron in hydrous phono-tephritic melts
- Amorphous materials: Properties, structure, and durability: Quantitative Raman spectroscopy: Speciation of Na-silicate glasses and melts
- Dissolution-reprecipitation of zircon at low-temperature, high-pressure conditions (Lanzo Massif, Italy)
- High-pressure behavior of gypsum: A single-crystal X-ray study
- Presence and zoning of hydrous components in leucite from the Alban Hills volcano, Rome, Italy
- Herderite from Mogok, Myanmar, and comparison with hydroxyl-herderite from Ehrenfriedersdorf, Germany
- Application of Raman spectroscopy to quantify trace water concentrations in glasses and garnets
- Neutron diffraction study of δ-AlOOD at high pressure and its implication for symmetrization of the hydrogen bond
- A simple predictive model for the thermal expansion of AlSi3 feldspars
- New data on PGE alloy minerals from a very old collection (probably 1890s), California
- High-pressure study on lead fluorapatite
- High-pressure Al-rich hexagonal phases—What are their kin?
- Leucite at high pressure: Elastic behavior, phase stability, and petrological implications
- Thermodynamic mixing properties of Rb-K feldspars
- Demicheleite, BiSBr, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy
- A lattice dynamical study of the aragonite and post-aragonite phases of calcium carbonate rock
- Water in natural olivine—determined by proton-proton scattering analysis
- Factors affecting heat transfer in natural SiO2 solids
- A solution model for high-temperature PbS-AgSbS2-AgBiS2 galena
- Incorporation of molybdate anion into β-FeOOH
- Disordering of Fe2+ over octahedrally coordinated sites of tourmaline
- Raman spectroscopy of CaIrO3 postperovskite up to 30 GPa
- The thermal behavior of richterite
- The crystal structure of kelyanite, (Hg2)6(SbO6)BrCl2
- Comparison of crystallographic orientations between living (Emiliania huxleyi and Gephyrocapsa oceanica) and fossil (Watznaueria barnesiae) coccoliths using electron microscopes
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