U 238 dating
Unfortunately, the breakdown of uranium creates radiation damage in the surrounding crystal, creating avenues for lead to escape.
The final point where the sample plots, will be some linear combination of the true concordia age and some final composition where lead diffusion stopped, either the present or some past metamorphic event.
Zircon is especially useful because it frequently contains uranium in substitution for zirconium, but does not incorporate lead (as shown by the absence of Lead-204).
Thus all the lead in the zircon can be assumed to be radiogenic.
Also, Lead 206 forms only from the decay of U-238 and Lead 207 only from the decay of U-235.
Uranium minerals themselves are too uncommon to be very useful in dating.
The most common dating method involves the use of minerals like zircon and monazite that are relatively common in granitic rocks.
Heaman and colleagues say their direct dating method can preclude the reworking process that relative chronology entails.
It is widely believed that all of the non-avian dinosaurs were wiped out in a mass extinction, known as the KT extinction event, that occurred between 65.6 and 66 million years ago in the late Cretaceous period.
Thus any of the radioactive isotopes and its lead daughter product can be used for dating, or a combination may be used.