The distribution of trace elements in chondritic meteorites. 2. Antimony, arsenic, gold, palladium and rhenium

Abstract

A radiochemical separation scheme for the isolation of the nuclides 76As (26.8 h), 109Pd (13.6 h), 122Sb (2.7 d), 188Re (17 h) and 198Au (2.7 d) from neutron irradiated geological materials was developed and was employed to study the distribution of arsenic, palladium, antimony, rhenium and gold in chondritic meteorites. Values for all five elements were obtained in the magnetic and non-magnetic fractions of eight bronzite, nine hypersthene and four enstatite chondrites as well as in six carbonaceous chondrites representative of all three classes. The results show that all these trace elements are predominantly siderophile in chondrites; significant quantities of antimony only were detected in the non-magnetic fractions. The values found in the metal phases of chondrites are confined to a much narrower range than the results for the same elements in iron meteorites. Mean values for these trace elements in bronzite, hypersthene and enstatite chondrite metal phases are distinctly different and none of the metal phase groups shows compositional similarities with iron meteorite structural groups. All the elements are depleted in hypersthene chondrites relative to bronzite chondrites, but only antimony can possibly be included as one of the group of “fractionated elements”. The results obtained here together with observations by other workers suggest that cosmic abundance figures in the mass region A = 105–125 should be raised.