The geochemical environment favorable for the formation of Precambrian banded iron ores is reconstructed and illustrated with results of experiments with the leaching of iron oxide and silica at different temperatures, at different pH ranges, and in the presence of certain elements in solution.It is suggested that the intermittent banding of silica and hematite in Precambrian banded ores is caused principally by the selective weathering of Precambrian soil. Due to the seasonal changes of temperature, amount of precipitation, and the alternately higher and lower pH range of the leaching solution, the Precambrian soil yielded alternately solutions carrying to the basin of deposition almost exclusively silica during the warm season and chiefly iron oxide during the cool period of the year.

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