Abstract
Neutron activation analysis has been used to determine the concentrations of Ru, Pd, Os, Ir, Pt and Au in seven carbonaceous and two enstatite chondrites. The average atomic abundances relative to 10 6 silicon atoms are tabulated below: Chondrite Ru Pd Os Ir Pt Au Group Carbon- aceous 1.84±0.09 6 1.32± 0.21 0.79± 0.12 0.76 ± 0.28 1.4 ± 0.25 0.18 ± 0.040 Enstatite 1.60 ± 0.08 1.23 ± 0.06 0−66 ± 0.01 0.25 ± 0.03 1.1 ± 0.00 0−19 ± 0.010 The data are compared with previously published precious metal values for olivine bronzite and olivine hypersthene chondrites. Abundances in olivine bronzite and carbonaceous chondrites are generally comparable except for Ir which is lower in the former group. Both the enstatite and olivine hypersthene chondrites have lower atomic abundances than the carbonaceous chondrites except for Au in the enstatite chondrites. The average depletion of precious metals in the olivine hypersthene chondrites relative to the carbonaceous chondrites is approximately 40%. As no obvious mechanisms for fractionation of precious metals during condensation of meteoritic matter are apparent, their abundances in carbonaceous chondrites should provide good estimates of the cosmic abundances of these elements.
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