Lake Superior iron ore basin

LAKE SUPERIOR IRON ORE BASIN (RU: Верхнего озера железорудный бассейн) is one of the largest iron ore basins within the world, which is situated at the western end of the Lake Superior, with its largest part at the north of the USA (the Minnesota, Wisconsin, and Michigan states), and the small part is within the limits of Canada (the Ontario province).

The extent of the basin from the west to the east is approximately 600 kilometres, while from the north to the south is approximately 300 kilometres. The deposits within the basin are concentrated within the 6 ore-mining regions: Mesabi, Vermilion, Cuyuna, Marquette, Menominee, and Gogebic. The iron ores within the basin have been discovered during the 1844, the regular extraction has been started since the 1854, the development was conducted using prevalently the underground method. The basin is situated on the southern periphery of the Canadian shield. The iron ores are confined to the Proterozoic (Huronian) iron ore formation, the thickness of which is from 15 to 300 metres. The ore-bearing strata are crumpled into the folds, are broken with the dip-slip faults, are riddled with the dikes and sills with the basic rocks. The ore bodies are represented by the magnetite quartzites, namely, by the taconites, and by the rich hematite ores, which are associated with these taconites, and which have emerged mostly as the result of the supergene leaching of the quartz of the taconites.

The rich ores either form the slightly inclined depositions on the taconites, or penetrate into these taconites as the pockets and deep wedges along the lines of the tectonic disturbances. During approximately 100 years, there were the object for the operation the rich hematite ores, which are containing 51-57% of the Fe element. During the 1854-1980, there have been extracted approximately 4.2 billion tonnes of the rich ores; the reserves of these ores have been significantly exhausted, and are tentatively estimated at 300-400 million tonnes. During the start of the 50-ies, together with the rich ores, there have been started to be developed the poor ores, namely, the magnetite quartzites with the average content of the Fe element of 27%. By the end of the 60-ies, these poor ores accounted for 50% of the marketable ore, which was obtained within this region, and during the 1980, these poor ores accounted for 85%.

The most significant group of the deposits, which are yielding more than 80% of the total extraction within the basin, is concentrated within the Mesabi region at the north-east of the Minnesota state, where it forms the belt with the length of approximately 160 kilometres, and with the width of 3-6 kilometres, which is stretching itself into the south-western direction. The mineralization is associated with the Proterozoic Biwabik formation, the rocks of which form the slightly inclined monocline with the north-eastern strike, with the dip of the rocks at the angles of 5-15 degrees. The thickness of the ore-bearing stratum is 100-220 metres. The sizes of the depositions with the rich ores vary, from the small lenses with the area of several tens square metres, to the large ore bodies, the area of which reaches 2.5 square kilometres. The extraction of the ore is conducted using the opencast method. The depth of the open-pit mines does not exceed 200-300 metres. The total reserves of the magnetite quartzites, which are suitable for the opencast development, are estimated at 16 billion tonnes. During the recent 15 years, the level of the extraction ranged within the limits of 60-90 million tonnes per year. The extraction of the ore was conducted at 34 mining enterprises, mostly using the open-pit mines (the share of the underground extraction accounts for less than 1%). The productive capacity of the largest enterprises (the Hoyt Lakes, Minnitaki, and Peter Mitchell) in terms of the marketable ore is 10-15 million tonnes per year, while in terms of the raw ore is 25-40 million tonnes per year. Practically all the ore, which is extracted, is being beneficiated. There are the major product from the processing of the ores the pellets, the production of which is conducted at 13 industrial plants with the total productive capacity of approximately 70 millio n tonnes per year. The major consumers are the metallurgical plants within the USA.