Directions of remanent magnetization in hematite ore deposits in the Precambrian banded iron formation of the Fort-Gouraud district, Mauritania, were investigated relative to their significance for determining the age and manner of formation of such ores. The hematite of the main ore zone in the F'Derik deposit appears to have been formed mainly when the enclosing beds were flat-lying, although a part exhibits a secondary magnetization which may have been acquired through remobilization during folding in later Precambrian time or by introduction of additional iron from some external source. The Rouessa West deposit includes soft hematite characterized by essentially random magnetic orientations and a capping of hard hematite with magnetization which is parallel to the present earth field. The magnetic data are consistent with the view that the soft ore represents residual accumulations formed by surface leaching (in part in geologically recent time) and that the hard capping was fo

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