Primary banded iron formation near Fort Gouraud, Mauritania, contains about 30 percent iron. Four kinds of hematite concentration (roughly 65 percent iron) are recognized. 'Deep hematite ore' is believed to be syngenetic, since it is chemically similar to the associated iron formation; its direction of remanent magnetism indicates that it is Precambrian and pre-structure, and it occurs as boulders in overlying Cambrian conglomerate. 'Hard surface ore' and underlying 'soft plaquette ore' are believed to be products of Tertiary weathering. 'Talus ores' have accumulated recently on some slopes.

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