High-grade ores, averaging more than 66 percent Fe and less than 1.5 percent H<2) O>+) , occur in Precambrian oxide-facies iron formation. The rocks are intricately folded, and metamorphosed to green schist or almandineamphibole facies. Ore bodies, some probably exceeding 400 million tons, are structurally controlled, but were formed after the deformation. Ore is believed to have formed by removal of quartz, replaced during metamorphism by hematite derived from the iron formation. Connate water from the sediments and magmatic water from intrusive granites are the most likely agents.

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