The crystal structures of synthetic Re‐ and PGE‐bearing magnesioferrite Spinels: Implications for impacts, accretion and the mantle

Abstract

Abstract. Re-and PGE-bearing magnesioferrite spinels were synthesized at oxidizing conditions between 0.1 MPa and 5.0 GPa, and 1150 to 1600 øC in equilibrium with Re-or PGEbearing metals and/or oxides. Electron microprobe analysis and single ciystal X-ray diffraction techniques were employed to determine the composition, crystal structures and site occupancies, indicating that the magnesioferrite structure can accommodate wt% levels of Re and the platinum group elements (PGE) at oxidized conditions. These results suggest that magnesioferrite spinels found in K-T boundary.

Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada 1 1Associate editor: R. J. Walker

“…Experimental studies on chromite-melt PGE partitioning indicate that IPGEs are preferentially incorporated into the spinel crystal lattice (Capobianco and Drake, 1990;Righter and Downs, 2001;Righter et al, in press). These data, coupled with high IPGE and low Pt and Pd abundances in chromite separates from a komatiitic lava lake (Puchtel and (Stone and Crocket, 2003), argue for chromite playing an important role in controlling the IPGE budget of mafic-ultramafic magmas and for its ability to fractionate IPGEs from Pt and Pd (see also reviews by Mathez, 1999, andCrocket, 2002).…”

The effect of oxygen fugacity on the partitioning of Re between crystals and silicate melt during mantle melting

“…While at lower f O 2 s their values of D sp=melt Re are within one order of magnitude of our values, their data deviate by several orders of magnitude from our results at more oxidizing conditions. Righter and Downs (2001) reported that Re is preferentially incorporated in magnesioferrite spinels, and that Re is compatible in magnetite. The three experiments reported by Righter et al (2004) at more oxidizing conditions show a dependence on the Fe content of spinel, but the scatter of the data is too large to warrant any conclusions.…”

“…For instance, Re is normally considered to be chalcophile (Burnham et al, 1998;Roy-Barman et al, 1998;Sattari et al, 2002), but an increasing number of experimental and empirical observations suggest that it might also be incorporated into silicate phases (Burton et al, 1999(Burton et al, , 2000Ertel et al, 2001;Burton et al, 2002;Fonseca et al, in press), especially garnet (Righter and Hauri, 1998). Additionally, under highly oxidizing conditions, magnetite and other Fe 3+ -rich spinels may potentially host large amounts of Re Righter and Downs, 2001).…”

Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

“…Oxide mineral separates from ore deposits are commonly enriched in HSE (Razin and Khomenko, 1969;Agiorgitis and Wolf, 1978;Page, 1984;Parry, 1984;Auge, 1988). Furthermore, many experimental studies (Krutzsch and Kemmler-Sack, 1983;Capobianco, 1993Capobianco, , 1998Righter and Downs, 2001) have produced HSE-rich oxides, showing the potential importance of these phases in hosting such elements. Whether the correlations between Ni and HSEs are due to olivine or chromian-spinel fractionation (or both), or require the fractionation of trace HSE minerals, has remained uncertain, but resolution of this question is important for a better understanding of HSE behavior in basic and ultrabasic systems (e.g., Puchtel and Humayun, 2001).…”

“…Righter et al ments were not saturated with either Re or a Re-oxide, the Re concentrations in the glass are variable and do not correlate with oxygen fugacity. The valence of Re may be 3ϩ or 4ϩ as suggested by its compatibility in spinels (Righter and Downs, 2001), or it may be higher, as suggested by its solubility in silicate melt as a function of fO 2 (Ertel et al, 2001). Glass from experiment 158A at the HM buffer and 1300°C contained 17 ppm Au and 82 ppm Pd (Table 8).…”