Eight whole-rock Rb–Sr age determinations on basement cores from the Hudson Bay Lowlands define an isochron of 1975 ± 45 m.y. (λRb = 1.39 × 10−11y−1) with an initial 87Sr/88Sr 0.7018 ± 0.0005. The indicated age is characteristic of the Churchill Province and on this basis Would suggest that the boundary between the Churchill and Superior provinces is to the south of the drill hole location. A similar age, 1925 ± 105 m.y. with an initial 87Sr/86Sr 0.7025 ± 0.0007, has been obtained on six whole-rock basement samples from the Minago River – Har-grave River area north of Lake Winnipeg.