Summary:
The Labrador Trough consists of Paleoproterozoic sedimentary and volcanic rocks, which extend along the eastern margin of the Archean Superior Craton to Ungava Bay. It forms the western part of a larger orogenic belt called the New Québec Orogen. In southwestern Labrador, the Labrador Trough extends into the younger Grenville Province, where the sedimentary rocks were deformed and metamorphosed.
Iron-ore deposits in the Labrador Trough are hosted in the Sokoman Formation, which sits toward the top of the shelf sequence, above a thick package of shale, dolostones, and siliciclastic rocks. The Sokoman Formation consists of a 30–170-m-thick sequence of cherty iron-rich sediments, and is continuous for 250 km from Labrador City to Schefferville; it also continues into Québec in both directions, and is one of the most extensive iron formations known on Earth. North of the Grenville Province, the stratigraphic sequence is largely intact, and the position and distribution of the Sokoman Formation are very predictable. Parts of this area experienced low-grade (greenschist facies) metamorphism and open to tight folding, but in the western foreland, the rocks are gently dipping and essentially undisturbed. In the southern part of the Labrador Trough, the rocks are highly metamorphosed and complexly folded, but the essential stratigraphy of the Kaniapiskau Supergroup remains discernable, albeit structurally disrupted. The productive unit in this area is locally known as the Wabush Iron Formation, but it is directly equivalent to the Sokoman Formation to the north.
Several large metataconite deposits are located in the Labrador City–Wabush area and adjacent Québec, and have been mined continuously since the 1960s. These deposits are all thought to represent a single stratigraphic horizon, and the economic deposits are largely developed by hinge-thickening and fold repetition.
In total, the Carol Lake deposits consist of 13 separate ore bodies, of which two are currently active (Humphrey Main and Luce). Individual deposits are associated with thickening of the magnetite–hematite schist on the closures of synforms and its repetition by complex isoclinal folds, which increase the aggregate thickness of deposits to approximately 400 m, in places.