Uranium geochemistry and fission-track mapping of phosphorites, Zefa Field, Israel

Heb. Univ., Dep. Geol., Jerusalem, Israel

Uranium concentrations and oxidation, 45 samples, Campanian. Optically anisotropic bone fragments have the lowest uranium concentration of all apatitic grains in the rock (80-150 ppm). Replaced isotropic bones are richer in U (120-260 ppm), as are isotropic ovulites (140-300 ppm). Nonapatitic grains and calcitic matrix and cement are U poor (usually less than 5 ppm). The ratio between U concentration in isotropic and anisotropic components in any rock is nearly constant around 1.6. The U/P ₂ O ₅ ratio in a sample depends on the uranium concentration in all grains rather than on the abundance of various grain types. Results are compatible with accepted models of phosphorite formation, according to which organic matter serves both as a phosphorus-contributing and uranium-concentrating phase.--Modified journal abstract.

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