Geologic models are developed for all mines to define the major ore and waste rock types. Computerized block models for iron ore are constructed that include all relevant geologic and metallurgical data. These are used to generate grade and tonnage estimates, followed by detailed mine design and life of mine operating schedules.

Mining and Pelletizing segment mines produce from deposits located within the Biwabik and Negaunee Iron Formation, which are classified as Lake Superior type iron formations that formed under similar sedimentary conditions in shallow marine basins approximately two billion years ago. Magnetite and hematite are the predominant iron oxide ore minerals present, with lesser amounts of goethite and limonite. Quartz is the predominant waste mineral present, with lesser amounts of other chiefly iron bearing silicate and carbonate minerals. The ore minerals liberate from the waste minerals upon fine grinding.

Proterozoic Lake Superior iron formations, Minnesota-Michigan, USA The Lake Superior region is the type locality for iron formations deposited together with conglomerate, quartzite and carbonate beds on the shelf of Archean cratons during and after the Great Oxidation of the Earth’s atmosphere and hydrosphere at ca. 2.4 Ga. This is the area where James (1954) developed his sedimentary facies model, and where Floran and Papike (1978) described the mineralogical changes and reactions with increasing metamorphic grade in the greenalite, minnesotaite, grunerite and ferrohypersthene zones of the Gunflint Formation, both landmark studies. Reviews of the Lake Superior iron ore district are in Lindgren’s textbook (1933) and in the Graton-Sales Volume 1: Ore Deposits of the United States 1933-1967, p. 489-549 (American Inst Min Metall Petrol Eng, New York, 1968). Past production from the Lake Superior district is 5.1 billion metric tons (1854-1990) compared to 3.7 billion tons from Krivoi Rog, Ukraine (Machamer et al. 1991).

The Mesabi Range contributed 70-75% of the total ore production. In 1965, direct-shipping ore contained 51-61% iron, and pellets produced from quartz-magnetite BIF 60-65% iron. Manganese-rich iron ore (5.6-14.8% Mn) was mined in the Cuyuna Range, contrasting with the low Mn-content of ore in the rest of the district (mostly < 1% Mn; Marsden 1968). Other publications include those of Goodwin (1956) on the petrography of the Gunflint BIF, Morey and Southwick (1993) on manganese in the Cuyuna Range, Morey and Southwick (1995) on stratigraphic correlation in the Lake Superior district, Morey (1999) on enriched high-grade ore (50-61% Fe) in the Biwabik BIF of the Mesabi Range, Farley and McKeon (2015) on Late Proterozoic-Paleozoic helium ages in botryoidal red hematite from the Gogebic Range, and Losh and Rague (2018) on the hydrothermal oxidation in the Biwabik iron formation by low-T (175°C) fluids expelled from the foreland basin during the 1.85 Ga Penokean Orogeny.

Oxide-facies Negaunee BIF, low metamorphic grade, Marquette mining district, Michigan. Folded hematite-quartz banded iron-formation. Dark blue-grey mesobands of specular hematite (0.5-1 mm, non-magnetic) alternate with red mesobands of hematite-stained chert (hard > steel). The legend by James reads: Jaspilite forming the upper part of the Negaunee Iron Formation of the Marquette district, Michigan, composed of red mesobands of chert stained by dispersed hematite and blue- grey mesobands of specular hematite. The outcrop is at Jasper Knob, Negaunee, Michigan.

All of iron ore mining operations are open-pit mines. Additional pit development is underway as required by long-range mine plans. Drilling programs are conducted periodically to collect modeling data and for refining ongoing operations.

Tilden Mine
The Tilden mine is located on the Marquette Iron Range in Michigan’s Upper Peninsula approximately five miles south of Ishpeming, Michigan. Over the past five years, the Tilden mine has produced between 7.6 million and 7.7 million long tons of iron ore pellets annually. Operations consist of an open pit truck and shovel mine.

Northshore Mine
The Northshore mine is located in northeastern Minnesota, approximately two miles south of Babbitt, Minnesota, on the northeastern end of the Mesabi Iron Range. Northshore’s processing facilities are located in Silver Bay, Minnesota, near Lake Superior. Over the past five years, the Northshore mine has produced between 3.2 million and 5.6 million long tons of iron ore pellets annually.

Mining is conducted on multiple mineral leases having varying expiration dates. Mining leases routinely are renegotiated and renewed as they approach their respective expiration dates. Northshore operations consist of an open pit truck and shovel mine.

United Taconite Mine
The United Taconite mine is located on Minnesota’s Mesabi Iron Range in and around the city of Eveleth, Minnesota. Over the past five years, the United Taconite mine has produced between 1.5 million and 5.3 million long tons of iron ore pellets annually.

Mining is conducted on multiple mineral leases having varying expiration dates. Mining leases routinely are renegotiated and renewed as they approach their respective expiration dates. United Taconite operations consist of an open pit truck and shovel mine.

Hibbing Mine
The Hibbing mine is located in the center of Minnesota’s Mesabi Iron Range and is approximately ten miles north of Hibbing, Minnesota, and five miles west of Chisholm, Minnesota. Over the past five years, the Hibbing mine has produced between 7.5 million and 8.2 million long tons of iron ore pellets annually.

Mining is conducted on multiple mineral leases having varying expiration dates. Mining leases routinely are renegotiated and renewed as they approach their respective expiration dates. Hibbing is an open pit mine.

Empire Mine
The Empire mine is located on the Marquette Iron Range in Michigan’s Upper Peninsula approximately 15 miles southwest of Marquette, Michigan. The Empire mine has had no production since the indefinite idle began in August 2016, compared to historically having an annual capacity of 5.5 million long tons of iron ore pellets. Prior to the indefinite idle, Empire Mine was an open pit operation.

Tilden
Operations consist of a concentrator that utilizes single stage crushing, AG mills, magnetite separation and floatation to produce hematite and magnetite concentrates that are then supplied to the on-site pellet plant.

Liberating the iron mineral requires that the crude ore be ground to the consistency of face powder. This process begins in the same way for both magnetite (metallic gray, below) and hematite (red-brown, below) as crude ore and water are fed into large primary autogenous mills. The term autogenous means that grinding media like the steel balls and rods used in some mills are not required. Instead, the tumbling action of the ore in the rotating mills is sufficient to reduce it to a consistency of beach sand. Tilden has twelve primary mills that are 27 feet in diameter and 14 ½ feet long.

Further grinding occurs in grinders and pebble mills which also operate autogenously. Grinders and pebble mills are, put quite simply, cylinders that continuously roll and turn. Inside them are rocks (ore) of various sizes.

The larger pieces of ore essentially act as grinders, crushing the smaller pieces into powder. As the larger pieces of ore ("pebbles") get comminuted in size, more large pieces are added. In the pebble mills, pebbles about 2 inches in size which are screened from the primary mill are used as grinding media. In grinders, larger rocks are used. Thus, grinders preceed pebble mills in the comminution process. The Tilden concentrator has twenty-four 15 ½ foot diameter pebble mills, each about 30 feet long.

Northshore
The crude ore proceeds to fine crushing where it is reduced to a three-fourths inch size or smaller. Following fine crushing, the ore is directed to dry cobbing, which is a dry magnetic separation process used to reject the portion of the ore that does not contain sufficient magnetic iron. The ore not rejected during dry cobbing is sent to a series of wet grinding and concentrating processes to separate, concentrate, and recover the iron from the incoming ore.

United Taconite
United Taconite operations consist of an open pit truck and shovel mine where two stages of crushing occur before the ore is transported by rail, operated by Canadian National Railway Company (CN), to the plant site. At the plant site an additional stage of crushing occurs before the ore is sent to the concentrator. The concentrator utilizes rod mills and magnetic separation to produce a magnetite concentrate, which is delivered to the pellet plant.

Hibbing
Hibbing operations consist of a concentrator that utilizes single stage crushing, AG mills and magnetic separation to produce a magnetite concentrate, which is then delivered to an on-site pellet plant.

Empire
Prior to the indefinite idle, operations consisted of a concentrator that utilizes single stage crushing, a concentrator that utilizes single stage crushing, AG mills, magnetic separation and floatation.

Cleveland-Cliffs Inc. has been a leader in iron ore mining and processing technology since inception. Cleveland-Cliffs Inc. produces various grades of iron ore pellets, including standard, fluxed and DR-grade.

Tilden Concentrator
Operations consist of a concentrator that utilizes single stage crushing, AG mills, magnetite separation and floatation to produce hematite and magnetite concentrates that are then supplied to the on-site pellet plant. From the site, pellets are transported by our LS&I rail to a ship loading port at Marquette, Michigan, operated by LS&I.

Concentrating Magnetite
First ground to a fine powder, the ore is next concentrated using magnetic separation and flotation to 60 to 65 % iron, then rolled into 3/8" dia pellets that are purplish-grey when they emerge, steaming, from the plants.

Concentrating Hematite
When processing hematite, Tilden must use a flotation system specially developed for the mine’s fine-grained or ........