Distribution of uranium and thorium among components of some chondrites

The distribution of uranium and thorium was studied in the fractionated components of several chondritic meteorites. A wet fractionation method was applied to separate the component mineral groups of powdered samples of two olivine-hypersthene chondrites, one olivine-bronzite chondrite, and three enstatite chondrites. Uranium was determined in four samples and thorium was determined in all six samples. Both element determinations were by neutron activation. Uranium was found to be enriched in the HCI soluble fraction of the hypersthene chondrite Bruderheim, and of the enstatite chondrites, Abee and St. Marks, whereas it was enriched in the HCI insoluble fraction of the bronzite chondrite, Richardton. On the other hand, thorium was found to be relatively concentrated in the HCl soluble fractions of enstatite chondrites and in the HCl insoluble fractions of all the ordinary chondrites we examined. In ordinary chondrites thorium behaves as a lithophile element, whereas in enstatite chondrites it seems to be partly chalcophile.