Amounts Of Platinum-group Elements Research Articles

Composition of Cosmic Spherules from Ferromanganese Crusts of the Magellan Seamounts

—2720 cosmic spherules extracted from ferromanganese crusts sampled at two guyots of the Magellan Seamounts were studied using a scanning electron microscope. In comparison with collections of modern cosmic spherules, our samples are significantly richer in I-type spherules (consisting of Fe oxides, often with a Fe–Ni metal core). The compositions of 406 metal cores were analyzed. Six spherules with cores significantly enriched in Co (>5 wt %) were found; these were the first spherules of this composition ever found worldwide. Such a high Co content in the cores cannot be explained by the evolution of a micrometeorite of chondrite composition at its melting. Some groups of the spherules have either elevated or lower Co concentrations than those expected according to the evolutionary trend of spherules at oxidation during the atmosphere entry. These groups apparently reflect the composition of the initial micrometeorites. It is proposed to use the composition of the cores of cosmic spherules to reveal the time variation in the composition of cosmic dust entering the Earth. Several spherules were found with small cores compared to the oxide shell; these cores are characterized by the presence of a significant amount of platinum group elements (PGE) (up to 2.4 wt % PGE). The averaged composition of PGE in the high-Ni core, which is the richest in PGE, shows a pattern close to that of chondrite. The collection contains 23 spherules that host PGE nuggets. In three spherules, micrometer-sized nuggets with various PGE were found (one nugget is Os + Ir + Ru, and two others contain all PGE). In 20 spherules, nanometer-sized nuggets of rhodium platinum were found. The largest nugget (3 μm) has PGE ratios close to chondritic, with the exception of a significant depletion in Pd.

Determination of Trace Amounts of Platinum Group Elements and Gold in Ultrabasic Rocks by Inductively Coupled Plasma Mass Spectrometry Using AG-X8 and LN-Resin Sorbents

A procedure is developed for determining trace amounts of Pt, Pd, Rh, Ru, Ir, and Au in ultrabasic rocks by inductively coupled plasma mass spectrometry. Chemical sample preparation included acid decomposition, separation of the main matrix components on an AG-X8 cation exchanger, and the subsequent separation of Zr, Hf, and Ta on an LN-Rezin complexing adsorbent. The limits of detection for Ru, Pd, Ir, Pt, Rh, and Au were 0.06, 0.2, 0.003, 0.4, 0.1, and 0.2 ng/g, respectively; the relative standard deviation in the determination of elements in the samples varies from 8 to 20% for Au, 2 to 9% for Pd, from 1 to 6% for Pt, from 1 to 4% for Ir, from 1 to 18% for Rh, and from 3 to 7% for Ru. The accuracy of the results is confirmed by their comparison with the published data for samples of HARZ01 harzburgite and OPY-1 ultrabasic rock, obtained in the framework of the international GeoPT program.

Platinum-group minerals from Seyba, Eastern Sayans, Russia, and substitutions in the PGE-rich pentlandite and ferhodsite series

AbstractChromitite zones associated with ultramafic units of the Lysanskiy layered complex of dunite–peridotite–gabbro composition could well represent the primary source for the placers bearing platinum-group minerals (PGM) of the entire drainage of the River Sisim and its tributaries, the rivers Ko and Seyba, eastern Sayans. Alluvial gold present in the placers of River Seyba, as elsewhere in the Sisim Placer Zone, reflects mineralisation during a recent period of tectonic activity. We focus on the PGM in the Seyba suite, and in particular on the attributes of pentlandite enriched in platinum-group-elements (PGE) and the compositionally similar and recently defined ferhodsite, which were trapped in host grains of Os–Ir–Ru alloy. Both minerals formed from small volumes of fractionated Fe–Ni–Cu melt considerably enriched in the PGE. In the Seyba suite, as in several others, the amounts of PGE in ferhodsite exceeds that in pentlandite, which results in a greater proportion of vacancies than in pentlandite.

Petrogenesis of the EET 92023 achondrite and implications for early impact events

AbstractWe report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low‐Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.

Petrology and geochemistry of Northwest Africa 5480 diogenite and evidence for a basin‐forming event on Vesta

AbstractWe performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact‐melt breccia from a target composed of olivine and pyroxene‐rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.

The Enrichment Mechanism of PGE and Characteristic of MSZ in HW Mining Area in Great Dyke Zimbabwe

Zimbabwe Great Dyke is a mafic-ultramafic lithosome intruded the Zimbabwe Craton. MSZ(Main Sulfide Zone) is the most important layer which contains substantial amount of PGE(Platinum Group Elements). PGE are concentrated in bottom of MSZ layer because of the intimate relationship between the content of Cu&Ni and enrichment of PGE. Acid vein rocks did not formed in the same period with the ore and adjacent rocks. Plenty of sulfide can be found in MSZ in pyroxenite, Sulfide in ore was owe to homogeneous of geochemistry process in the magamtic segregation cycle, while them in gabbro and fractures were simply by the post magmatic thermal solution activities.

Partitioning of platinum group elements in the Fe‐O‐S System to 11 GPa and their fractionation in the mantle and meteorites

The partitioning of minor amounts of platinum group elements (PGE: Ru, Rh, Pd, Os, Ir, Pt) in the Fe‐O‐S system has been investigated to 11 GPa. The marked fractionation of Pt from Pd in the presence of coexisting alloy and sulfide liquid, reported earlier for the Fe‐Ni‐S system at low pressure, is extended to high pressure. The experiments were carried out at 1000°–1375°C and 4.5–11 GPa with graphite capsules using 18‐mm octahedral pressure cells in a uniaxial split‐sphere multianvil apparatus. Oxygen fugacities corresponded to wustite stability. Phases present included sulfide liquid (close to M3S2 stoichiometry), FeS (troilite, pyrrhotite, HPP), alloys (PtFe, PtFeIr, OsIr, FePtIrOs, OsFeIr), and wustite. Partition coefficients for OsIr alloy/Fe1−x S at 1200°C, 11 GPa are Os (1400), Ir (160), Pt (32), Ru (0.6), Rh (0.2), and Pd (0.04) and for FePtOs alloy/liquid at 1100°C, 8.5 GPa are Os (120), Ir (82), Pt (20), Ru (5.0), Rh (1.6), and Pd (0.1). Geochemical processes which involve separation of a metal‐rich phase from sulfide therefore would result in fractionation of PGE, with Os, Ir, and Pt concentrated in the former phase and Pd in the latter. These results are further support for the presence of a discrete metal‐sulfide liquid during the primary differentiation of planetary material and preclude an explanation for the fractionation of PGE in chromitites and mafic crustal rocks based on equilibrium partitioning between refractory alloys in residual assemblages and immiscible sulfide liquid in silicate melts.

Anodic characteristics of amorphous nickel-value metal alloys containing small amounts of platinum group elements in 0.5 M NaCl

By utilizing the characteristics of amorphous alloys capable of possessing specific electrocatalytic activity and corrosion resistance by alloying and surface activation treatment, an attempt was made to find amorphous alloys which are active as the anode material for production of sodium hypochlorite by electrolysis of seawater. Amorphous Ni-Nb and Ni-Ta alloys containing only 0.5–2.0 at % palladium and other platinum group metals showed a very high activity for chlorine production by electrolysis of 0.5M NaCl at 30°C when they were previously immersed in 46% HF for surface activation. The current efficiency of these surface-activated alloys for chlorine evolution considerably exceeded that of the currently used, most active Pt-Ir/Ti electrode for electrolysis of seawater. The surface activation treatment resulted in preferential dissolution of alloy constituents unnecessary for the electrocatalytic activity, i.e. nickel and valve metals, with a consequent enrichment of electrocatalytically active platinum group elements in the surface-activated layer. The corrosion weight loss of the surface-activated amorphous alloys under the steady state conditions for chlorine production was undetectable by a microbalance.