Central Range Mining

Central Iron Range Geology

Over 1 1/2 billion years ago when a vast, shallow sea covered much of the area which we know today as Northeastern Minnesota. The great  Mesabi Range began in this sea, which contained concentrations of iron and silica. The iron and silica settled to the bottom of the sea and formed thick layers of iron-bearing sediments. As time went on, the sea disappeared leaving these iron-bearing sediments buried under thousands of feet of sand, clay and mud. As a result of this deep burial, the iron-bearing sediments were subjected to heat and pressure which transformed them into a hard, flinty rock which we call taconite. Tacointe consists primarily of chert, a form of silica, and of magnetite, a black, magnetic iron mineral.

The Mesabi Range, largest of three iron ranges in Minnesota, consists of a thick layer of taconite extending from Babbitt on the east, 110 miles southwest to Grand Rapids. The taconite varies from one to three miles in width and up to 500 feet in thickness.

During the long period since its formation, Mesabi taconite has been subjected to a variety of geologic processes which have altered its character. Certain areas of taconite were affected by solutions which dissolved out portions of the silica, and the black magnetite was converted to red hematite or what we call "natural" ore. These natural ore mines, scattered throughout taconite of the Mesabi Range like raisins in a cake, played an important part in Minnesota's history. In some area, particularly on the western end of the Mesabi Range, magnetic taconite has been changed to red hematite, leaving the silica essentially unchanged, forming non-magnetic taconite and what we call "semi-taconite". However, the great bulk of the Mesabi Range iron formation remains as hard, magnetic taconite, enough to last hundreds of years using conventional mining methods.