SHRIMP dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition. Thus, xenotime dating has significant economic application to Pre-cambrian sediment-hosted ore deposits, such as Witwatersrand Au-U, for which there are no precise depositional ages. The growth history of xenotime in the Witwatersrand Supergroup is texturally complex, with several phases evident. The oldest authigenic xenotime Pb-107/Ph-206 age obtained in sandstone underlying the Vaal Reef is 2764 +/- 5 Myr (1 sigma), and most likely represents a mixture of diagenetic and hydrothermal growth. Nevertheless, this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition. Other xenotime data record a spread of ages that correspond to numerous post-diagenetic thermotectonic events (including a Ventersdorp event at approximate to 2720 Ma) up to the approximate to 2020 Ma Vredefort event.