Abstract

Two parallel beds of metamorphosed Precambrian iron formation located within the Goe Range area of the central coastal region of Liberia are described. These beds consist of itabirites and silicate iron formation. They are associated with schists and quartzites which are metamorphosed mature pelitic sediments and cherts. The chemistry of the iron formation is similar to that of other middle Precambrian iron formations except for higher phosphorous and aluminum content. Relative concentrations of Al and P tend to coincide in layers conformable with structure and bedding.Ore concentrations in which iron content reaches a maximum of 65% are described. Such concentrations are not generally formed over silicate rich horizons. Controls of ore localization are mineralogy, grain size, structure and width of iron formation. Leaching of quartz from iron formation by meteoric waters is associated with intermittent lateritization of surface zones. Lateritization has caused surface enrichment in alumina, and mobilization of iron. The 5-10 meter thickness of the alumina enriched goethite capping indicates the depth to which Eh and pH fluctuations are significant.Supergene waters remove quartz from iron formation, leaving a residual mass of soft or biscuit ores under the surface capping. The ores persist in the largest concentrations to depths of more than 100 meters.

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