The largest of four Iron Ranges that stretch across northeastern Minnesota and the Upper Peninsula of Michigan, the Mesabi Range is 110 miles long, angling WSW to ENE between Grand Rapids and Babbitt, Minnesota. Up to 3 miles wide, this chain of low hills was heavily mined for its rich load of iron ore throughout the first half of the 20th Century, peaking during the military buildup of WWII. Today, most of its high grade hematite has been recovered but a new boom to mine taconite, a lower grade ore, is underway; while hematite is 70% iron, only 30% of taconite is composed of hematite and magnetite, requiring enrichment via pulverization, the use of binding agents and the final production of taconite pellets (65% of each pellet is pure iron).
While iron is widespread across the globe, composing 5% of Earth's crust and coloring the red-rock country of the American West and central Australia, mineable deposits of iron ore are relatively rare, having formed within ancient Precambrian rock (1.6-3.0 billion years ago). Most geologists believe that the iron of the Mesabi Range initially eroded from Precambrian mountains and collected within the basin of a shallow sea; there, oxygen produced by early forms of photosynthetic algae and bacteria, converted the free iron deposits to iron oxide. Up to 500 feet thick, most bands of the hematite run close to the surface in the Mesabi Range and open pit mines produced the majority of the ore.
Now barren, many of the Mesabi mine pits have become man-made lakes, stretching south of the numerous glacial lakes that speckle the Arrowhead of Minnesota. Almost 3 billion years after it formed in Precambrian seas, most of the Mesabi iron ore has dispersed across the globe, now trapped within the steel framework of skyscrapers and the thick hulls of battleships.
