The Sudbury Basin
A ring of low hills, with Sudbury on the south rim, follows the outline of the "Sudbury Nickel Irruptive", a unique and remarkably complex geological structure. The mines situated along the outer rim of this boat-shaped basin produce most of the world's nickel, platinum, palladium and related metals, and large amounts of copper, gold, tellurium, selenium and sulphur. Made up of many kinds of igneous rock forced while still molten into a roughly concentric arrangement, some seventeen hundred million years ago, the basin is about 59 km long and 27 km wide. These rocks and the minerals of the ore deposits probably had a common source deep within the Earth's crust.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.