Fe, Ni and Co variations in the metals of some antarctic chondrites

Abstract

Nearly 4,000 Fe, Ni and Co analyses have been carried out on the metal phases of 12 Antarctic chondritic meteorites by means of the electron microprobe. H-group chondrites show relatively simple patterns of variation for these elements but L- and LL-group members show much more scatter in both Ni and Co concentrations. A single member of the CO3 group investigated shows some scatter in the concentrations and also much higher Co concentrations in the high-Ni (awaruite?) phase (1.25–2%) than in the coexisting kamacite (0.2–0.5%). Thus, analysis of the metal phases can provide not only a means of identifying the group to which a meteorite belongs, but also the possibility of distinguishing between individual chondrites from the same group. The overall concentrations of Co in the metal particles in the different groups are considered to be related inversely to the abundance of metal grains in meteorites of these groups while the scatter is interpreted as reflecting characteristics inherited at the time of accretion. The absence of homogenisation of the concentrations of Fe, Ni and Co in the metal particles, even in so-called equilibrated chondrites, provides further evidence against the widely held notion that these meteorites have been involved in a high-temperature prograde metamorphism.