GEOLOGY OF BIWABIK IRON FORMATION, DUNKA RIVER AREA, MINNESOTA

Review of literature on the studies of iron formation shows that quartz and magnetite are the most abundant minerals in the iron-formation, but iron-rich silicates that formed during metamorphism are common. Orthopyroxene, Ca pyroxene, fayalite, cummingtonite, and hornblende are the most abundant silicates. The metamorphism was isochemical except for the loss of the original H//2O and CO//2. The original carbonates and phyllosilicates were converted principally to pyroxenes and fayalite. The amphiboles formed mainly during retrograde metamorphism from the pyroxenes and fayalite. The quantity of magnetite did not change appreciably during metamorphism, whereas part of the original quartz was consumed by reaction with the carbonates.