Analyses and interpretation of Rb-Sr data on 17 granite and porphyry pebbles from the White Lake metaconglomerate indicate a maximum possible age for the source rocks of the clasts at 2885 ± 160 m.y. However, we favour a more conservative interpretation of our data as, simply, older than 2670 m.y., and also we caution against the use of these data to support the existence of a pre-Kalgoorlie System granitic basement. The lower limit for the age of the conglomerate is 2550 m.y., imposed by a Rb-Sr age on a biotite from the matrix of the conglomerate. Another control on the minimum age of the metaconglomerate is 2620 ± 20 m.y. imposed by the isochron for the Mungari granite, which is considered as younger than the White Lake metaconglomerate.