Comparison of the isotopic abundance of U235 and U238 and the radium activity ratios in Colorado Plateau uranium ores

The isotopic abundances of uranium and the radium activity ratios of eleven samples of uranium ore from the Colorado Plateau have been measured. No significant variation in the isotopic abundance of the uranium was noted; with'in the experimental error, the average U²³⁵/U²³⁸ ratio is 137.7. There is a significant variation in the Ra²²⁶/Ra²²³ activity ratios (0.048−0.143), which indicates a relatively recent alteration of the ore samples. The variations do not, however, explain the lead-uranium and lead-lead age discrepancies.