The chemical composition of metallic spheroids and metallic particles within impactite from Barringer Meteorite Crater,Arizona

Atomic absorption analyses of 25 metallic spheroids from Barringer Meteorite Crater have been carried out for Fe, Ni, Co and Cu. In addition, electron microprobe analyses of 58 impactite metallic particles have been carried out for Fe, Ni and Co from four different impactite samples. The normalized Ni, Co and Cu contents of the spheroids were from 13–22 per cent, 0.8–1.3 per cent and 260–430 μg/g, respectively. These figures represent enrichment factors of 2–3 in the spheroids compared to analyses of the bulk meteorite. The Co/Ni and Cu/Ni ratios in the spheroids are close to the respective ratios in the bulk meteorite. This suggests that the spheroids were formed by preferential removal of iron by oxidation from a chemically homogeneous liquid.The impactite metallic particles had Ni contents from 10 to 95 per cent and Co contents from 0·3 to 4 per cent. The Co contents of these particles showed a positive correlation with Ni up to 60 per cent Ni and a negative correlation beyond 60 per cent Ni. Reaction of the impactite metallic particles with SiO₂ of the target can explain these variations. Our findings show that extensive chemical reaction between projectile and target occurs at impact.