STUDIES OF THE CONTENT AND THE DISTRIBUTION OF URANIUM OF LUNAR MARE BASALTIC FRAGMENTS TAKEN BY APOLLO 17

The U-content and the U-distribution in 70017-291 lunar mare basalts was studied by means of fission tracks.The pure moscovite sheets and "Lexan" polycarbonate foils were used as track detectors.The samples were irradiated in the thermal column of the heavy-water reactor,Institute of Atomic Energy,Academia Sinica.After irradiation,the moscovite sheets and Lexan foils were removed,then etched in 40% HFat 25℃ for 20 minutes and in 6 N NaOHat 70℃ for 10 minutes respectively.The U-eoncentra-tions in basaltic fragments range from 3.0 ppb to 43.4 ppb,and in pyroxene from 0.95 ppb to 15 ppb.From the data of pyroxene,a tendency of decreasing U-concentra-tion with increasing crystal size is recognizable.The U-microdistribution pattern of rock fragments shows that uranium is mainly concentrated in intergranul,ar material.The higher the silicon content,the higher the U-content.These are obviously due to the fact that the residual liquid would be isolated prefer ably in the final stage of crystallization,and it is highly enriched in uranium.