Kenneth R. Ludwig 1977 <p>Most calculations of U-Pb isotope apparent ages are made by use of equations that assume initial secular equilibrium of the uranium decay-chains. The possible error in calculated Pb/U isotope ratios arising from this assumption (especially for ores of sandstone uranium deposits) can be over 10 percent at 1 million years and exceed analytical error even at a 30 m.y. apparent age. Use of the more general equations (adapted from the Bateman equations) is desirable for calculation and interpretation of U-Pb isotope apparent ages of both open and closed systems in the range of 2 to 20 m.y. and is essential for apparent ages less than about 2 m^y. For very young sandstone uranium deposits, a significant uncertainty in the ²⁰⁸Pb/²³⁸U systematics may still persist owing to the uncertainty in the initial value of ²³⁴U/²³⁸U.</p> application/pdf en U.S. Geological Survey Effect of initial radioactive-daughter disequilibrium on U-Pb isotope apparent ages of young minerals article