The name « Fenimore Iron Formation » was used in the 1950s to refer to a regionally significant iron formation outcropping SW and west of Ungava Bay (Owens, 1952). The name comes from the name of the Fenimore Iron Mines Ltd. company, which was exploring for iron in the northern Labrador Trough at the time. Bérard (1965) gave the unit the rank of formation.

According to Bérard (1965), the Fenimore Formation overlies the Alison Formation (now abandoned) in « paraconformity » and is in turn overlain by the Dragon Formation (now abandoned), also in « paraconformity ». In places, the Chioak Formation overlies the Fenimore Formation with an unconformable contact. The maximum thickness of the latter is 45 m between latitudes 58°N and 59°N (Bérard, 1965), but it is 150 m further south near the Mélèzes River (Bergeron, 1954).

The Fenimore Formation was described in detail by Owens (1952, 1955) and Bérard (1965). Owens (1952) divided the iron formation into eight subunits: 1) finely bedded jasper or chert; 2) metallic iron formation (hematite and magnetite); 3) very finely bedded cherty (grey or white) iron formation; 4) granular silica (quartz) iron formation; 5) carbonate-facies iron formation (ankerite-siderose, with grey-brown chert interstratifications and nodules); 6) iron formation with either magnetite or chert-rich interstratifications; 7) spotted silica iron formation (fine quartz, with carbonate spots); and 8) conglomeratic iron formation (iron formation fragments).

Bérard (1965) recognized seven main facies that make up the iron formation: 1) speckled quartzite; 2) jaspilite in thin to thick beds; 3) brown or blue carbonate ironstone; 4) siliceous breccia; 5) hematite and magnetite ironstone; 6) silica-magnetite ironstone; and 7) magnetite-sulphide argillaceous schist. A layer of magnetite-sulphide schist separates the Fenimore Formation from the underlying Alison Formation. Speckled quartzite forms the upper member of the formation. The stratigraphic order of the other facies is variable (Bérard, 1965). Nevertheless, the general order of facies is as follows (from bottom to top): sulphide facies, oxide facies, carbonate facies (with interbedded silicate facies) (Bérard, 1965).

Bérard (1965) did not comment on the equivalence, or otherwise, of the Fenimore Formation with the Sokoman Formation. However, he did note that the Alison Quartzite (Wishart Formation), which underlies the Fenimore, is probably equivalent to the Wishart Formation in the southern Trough. South of the study area of Bérard (1965), an iron formation that appears to represent the continuation of the Fenimore Formation was mapped as the Sokoman Formation by Clark (1979). Thus, it can be concluded that the Fenimore and Sokoman formations are homotaxial and therefore equivalent. Because of this equivalence, Clark and Wares (2004) recommended that the name Fenimore Formation be abandoned.

Based on similar stratigraphic relationships, the Fenimore Formation is probably the stratigraphic equivalent of the Sokoman Formation in the southern Trough. Because the use of the name Sokoman Formation preceded that of the Fenimore Formation (see Frarey and Duffell, 1964), the former must take precedence. The name Fenimore Formation was abandoned, as recommended by Clark and Wares (2004).

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