Within the Pilbara Block of Western Australia, a complex of migmatite, gneissic and foliated granite near Marble Bar is intruded by a stock of younger massive granite (the Moolyella Granite) with which swarms of tin‐bearing pegmatites are associated. The age of the older granite has been determined by the Rb‐Sr method as 3,125 ± 366 m.y., and that of the Moolyella Granite as 2,670 ± 95 m.y. Initial Sr87/Sr86ratios suggest that the older granite is close to primary crustal material, but that the Moolyella Granite consists of reworked material. It probably formed by partial remelting of the older granite.