Abstract
The U-distribution in selected basaltic fragments from lunar fines 10084, rocks 12021 and 12053 and breccias 14305 and 14321 was studied by means of fission tracks in mica detectors. U-enriched mineral phases were localized with an accuracy of better than 1 μm by applying a photographic mapping technique. Identification and elemental analysis were carried out using an electron microprobe. Phases of high U-content were identified as apatite (30–280 ppm), SiO 2-rich glasses (3–150 ppm) or fine-grained Zr-containing minerals of grain sizes < 1 μm (50–450 ppm). These U-enriched phases preferentially occur in the mesostasis. An inverse relationship was found between the U-concentration and the volume of the mesostasis regions. The ratio of the U-contents of the residual liquid and the major phases is comparable with that found in terrestrial basalts.
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