• Surface mining or open-pit mining
• Underground or shaft mining
To be competitive, iron mining must be done on a very large scale. Surface mining is the preferred choice, although there are exceptions. Small, low-capacity mines have rapidly disappeared.
In 2000, twelve iron ore production complexes with 12 mines, 10 concentration plants, and 10pelletizing plants were operating in Minnesota, Michigan, and six other States. The mines included eleven surface and one underground operation. Virtually all ore was concentrated before shipment. Nine mines operated by five companies accounted for 99 percent of production.
When the iron ore lies close to the surface, it often can be uncovered by stripping away a layer of dirt, sometimes only a few feet thick. The ore is mined from large open pits by progressive extraction along steps or benches. The benches provide access to progressively deeper ore, as upper-level ore is removed. After the soil and overlying rock are cleared, the ore is drilled and blasted. The portion of the ore body to be removed is first drilled in a specific pattern, and the holes are loaded with explosive mixtures and blasted. Following blasting, the fractured ore is
loaded by huge electrical shovels, hydraulic excavators, or front-end loaders onto large dump trucks. The wide holes in the ground created by drilling, blasting, and ore removal are referred to as “open pits”.
Underground mines are established in areas with promising ore deposits. Iron ore deposits may lie deep underground. A shaft must be dug from the surface and an elevator or hoist must be installed. The shaft is the primary vertical channel through which people and ore are transported in and out of the mine. It may be desirable to sink a vertical shaft in barren wall rock at one end or to one side of the ore deposit to keep haulage and hoisting facilities clear of actual underground mining while minimizing haulage of ore underground to the mine exit. The miner’s elevator is called a cage and the ore reaches the surface via a car called a skip. A ventilation system near the main shaft ensures that miners receive fresh air and prevents the accumulation of dangerous gases. Miners cut tunnels (drifts) branching out from the shaft at various levels to access the veins of ore. These levels are, in turn, connected by openings called raises. Stopes are the chambers in which ore is broken and mined. Cars or other conveyors carry the ore to the shaft, where it is hoisted to the surface.
The basic mine plant for underground mining operations consists of headframe, hoist, timber framing and storage area, miner’s change house, compressor house, machine shops, warehouse, office, ore storage, ore loading, and shipping facilities.
Most iron ore leaves the mine by rail, after which, much is transferred to ships. A much larger proportion of ore is moved by water in the United States than elsewhere because of the proximity of the mines to the Great Lakes, which offer low-cost transportation. No U.S. taconite mine is more than about 100 miles from the Great Lakes, and most are much closer. A lesser-used method of transportation is an iron ore slurry pipeline