Ir Enrichment Research Articles

Abundance and distribution of palladium, platinum, iridium and gold in some oxide minerals

Palladium, platinum, iridium and gold were determined in chrome-spinel, ilmenite and magnetite samples from mafic and ultramafic layered complexes (Bushveld, Stillwater, Rhum, Rhochrome Mine in Zimbabwe and Chambers Mine in the U.S.A.) and in alpine-type deposits (Greece, Pakistan and Turkey). Purified mineral samples (50–100 mg) were analysed by neutron activation after a radiochemical ion-exchange separation. The abundances of the individual platinum group elements were similar in all the chrome-spinels (Pd and Pt = 50–500 ppb, Ir = 10–100 ppb, Au = 0.5–5.0 ppb) with the exception of the alpine-type deposits where the chrome-spinels were depleted in Pd and Pt (often < 50 ppb). Ilmenite and magnetite samples from the Bushveld Complex were enriched in all the elements, which were in a constant ratio but distributed heterogeneously. Analyses of coexisting chrome-spinel and silicate in the Rhum Layered Intrusion showed that Pd, Pt and Au are concentrated at the mineral grain boundaries. There is a two-fold enrichment of Ir in the spinel phase. It is proposed that the platinum group elements do not substitute for base metals in the chrome-spinel or other oxide phases but that they tend to remain in the magmatic fluid until they finally crystallise at overgrowths on grain boundaries of the cumulus oxide.

Strangways Crater, Northern Territory, Australia: Siderophile element enrichment and lithophile element fractionation

The Strangways Crater, Northern Territory, Australia (15°12′S, 133°35′E), has a central core, about 10 km in diameter, of shocked granitic gneiss and amphibolite, and some remnants of a melt rock sheet, surrounded by outer rings of quartzite and siltstone to a diameter of 20–25 km. Seven samples of melt rock (six granitic melts, one shale melt clast) and four samples of country rock (granitic gneiss, amphibolite, shale, quartzite) were analyzed by neutron‐activation analysis: for Sc, Cr, Fe, Co, Zn, Rb, Zr, Sb, Cs, Ba, rare earth elements, Hf, Ta, Th, and U, the samples were analyzed instrumentally; and for Ni, Se, Pd, Ag, Cd, Re, Os, Ir, and Au, they were analyzed radiochemically. Siderophile elements are significantly enriched in the granitic melt rocks relative to country rocks; for example, the Ir enrichments range from 0.6 to 2.8 ppb. The low Ir/Ni ratio (∼0.16 relative to C1 chondrites) excludes a chondritic impacting body, and Cr enrichment argues against impact by an iron meteorite. The Strangways Crater may have been formed by the impact of an olivine‐rich achondrite and melt rocks appear to contain about 3 wt.% of projectile material. The composition of the granitic melt rocks cannot be reproduced by any simple mixture of analyzed country rock types and chemical fractionation by selective shock melting appears to have taken place.

Meteoritic material at four Canadian impact craters

Eleven impact melt and 6 basement rock samples from 4 craters were analyzed by neutron activation for Au, Co, Cr, Fe, Ge, Ir, Ni, Os, Pd, Re and Se. Wanapitei Lake, Ontario: the impact melts show uniform enrichments corresponding to 1–2% C1-chondrite material. Interelement ratios ( Co Cr , Ni Cr , Ni Ir ) suggest that the impacting body was a Cl-, C2-, or LL-chondrite. Nicholson Lake, North West Territory: Ni, Cr and Co are distinctly more enriched than Ir and Au which tentatively suggests an olivine-rich achondrite (nakhlite or ureilite). Gow Lake, Saskatchewan and Mistastin, Labrador: small enrichments in Ir and Ni; both the low Ir Ni ratios and low Cr content suggest iron meteorites, but the signals are too weak for conclusive identification. A tentative comparison of meteoritic signatures at 10 large, ≥4km craters and their presumed celestial counterparts (13 Apollo and Amor asteroids) shows more irons and achondrites among known projectile types, and a preponderance of S-type objects, having no known meteoritic equivalent, among asteroids. It is not yet clear that these differences are significant, in view of the tentative nature of the crater identifications (achondrites in particular), and the limited statistics.

Deactivation of alumina-supported nickel and ruthenium catalysts by sulfur compounds

The kinetics of sulfur deactivation of alumina-supported nickel and ruthenium catalysts are examined under methanation conditions in the presence of low concentration of H 2S (<10 ppm) added to the feed stream ( H 2 CO = 4 1 ) . Based on a theoretical analysis of catalyst deactivation by irreversibly adsorbed surface sulfur atoms, we calculate the deactivation rate constants for the poisoning process. The Ru Al 2O 3 catalyst exhibits a higher poisoning rate constant than Ni Al 2O 3 . The catalytic properties of Ni Al 2O 3 are greatly modified by the addition of low concentrations of Ir. The Ni Ir Al 2O 3 catalyst exhibits higher methanation activity and greater resistance to sulfur deactivation. Temperature-programmed desorption and surface reaction studies indicate the formation of new binding states for CO adspecies on the surface of the Ni Ir catalyst. Surface composition measurements by means of Auger electron spectroscopy demonstrate considerable Ir enrichment on the surface of the Ni Ir Al 2O 3 catalyst.

Lunar crater Copernicus: search for debris of impacting body at Apollo 12 site

In an attempt to characterize meteoritic material at the Apollo 12 site, 4 KREEP concentrates from soil 12033 have been analyzed by neutron activation analysis. These contain a meteoritic component in which siderophile Ir, Re and Sb are depleted by about a factor of 2, while volatile Se, Zn, Ag and Bi are depleted by a factor of more than 5 relative to Au. This pattern does not closely resemble any major chondrite or iron meteorite group, but is very similar to that observed in high-alkali samples from Apollo 14. The meteoritic component in KREEP at both sites is therefore predominantly derived from Imbrian ejecta. However, a second, small component of primitive composition seems to be present in Apollo 12 KREEP, judging from the slight, uniform enrichments in Ir, Re, Sb, Se and Zn relative to Au. This component does not seem to be due to micrometeorites. If it is attributed to the Copernican projectile, the crater Copernicus may have been formed by a cometary nucleus, 4 km in diameter, with an impact velocity of 30–40 km/sec. These conclusions depend critically on the assumption that the meteoritic component in Apollo 12 KREEP is representative of the entire impact.