Rb‐Sr whole rock analyses describe the isotopic system of the Mount Edgar Batholith in the Archaean Pilbara Block, Western Australia. The batholith comprises a complex gneiss terrain intruded by ‘older’ variably deformed granites, minor aplite, and a ‘younger’ post‐tectonic granite, the Moolyella Suite. The ‘older’ granites occur as six suites with isotopically indistinguishable individual isochrons; the pooled mean age is 3202 ± 17 Ma with initial87Sr/86Sr ratios in the range 0.7010–0.7025. This age is taken to record timing of granite emplacement, although it may represent a metamorphic resetting. If the latter is correct, resetting took place in the greenschist to lower amphibolite facies, less than 100 Ma after batholith formation. Localized Rb‐Sr resetting and aplite dyke emplacement record a ∼3000 Ma event also detected in other parts of the Pilbara Block. The ‘younger’ Moolyella suite is dated at ∼2800 Ma, but appears to have undergone minor isotopic disturbance.