Trace element content of metals from H- and LL-group chondrites

Abstract

The content of Ni, Co, As, Au, Ir, Os, Re, Pt and Ru in metallic fractions of H- and LL-group chondrites has been determined via instrumental neutron activation analysis. The amount of these elements varies with the grain size of the metal, as a result of the presence of kamacite in the coarse and of taenite in the intermediate and fine fractions. The refractory siderophile elements Ir-Ru increase in amount with decreasing grain size of the metal, independently from petrologic type, but Re appears to redistribute more easily than the other refractory metals at higher recrystallization temperatures, diffusing from taenite into kamacite. Refractory metals are fractionated in ordinary with respect to carbonaceous chondrites in the order Ir < Ru < Pt < Os < Re. The ratios of Au, As and Co to Ni are constant in the three groups of ordinary chondrites, suggesting that these elements were already condensed before the metal-silicate fractionation process took place.