The mines on the Mesabi Range historically extracted hematite, a rusty-red gravel-like ore. Hematite contained 50–70% iron and could be dug out of the ground and shipped right out to be made into steel. From 1890 to about 1980, 2.5 billion tons of this ore was mined here, but these “natural ores” were largely depleted by the 1980s.
Landsat images acquired after 1984, however, show continued expansion of the open-pit mines. The rock being mined now is a lower grade ore called taconite, which has about 25–30% iron content. Taconite is a hard, dense rock containing a mixture of silicates and magnetite and is abundant on the Mesabi Range.
New processing methods developed in the mid-20th century made taconite mining profitable. After it’s mined, the taconite is crushed into a fine powder. The magnetite is separated with magnets and agglomerated into marble-sized pellets. The finished pellets contain over 65% iron. These pellets are shipped to steel mills.
Because only about one-third of the magnetite is used in the taconite production process, large amounts of tailings are generated. While the open-pit mines are visible in Landsat images, it’s the large pink/purple areas—the tailings basins—that really stand out because they take up more area.
Tailings flow as slurry into these basins, which are bounded by earthen dikes. Taconite tailings particles range from the size of clay to sand. Some of the tailings may be mined again as technology develops to remove any remaining iron.
The USGS aerial photo from 1953 includes a portion of the area shown in this Landsat series. The urban areas are the towns of Virginia and Eveleth. The historical aerial photos extend the imagery record back at least two decades further than the Landsat scenes. Using these photos from the collection at EROS, we can see the mining activity and associated land changes even earlier than the Landsat record.