Hematite ores of Lower Vulcan are non-banded, commonly oolitic, and contain sedimentary breccias and clastic quartz grains. Magnetite ores of Upper Vulcan are well-banded, oolites (recrystallized chert) are sparse, and clastic quartz is rare or absent. Middle Vulcan has intermediate types. The correlation between mineralogy and texture suggests that the facies differences are of primary sedimentary origin (hematite facies in shallow water, magnetite facies in quiet stagnant water), though the magnetite itself may represent diagenetic reduction by organic matter.

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