One is China.
From my research, it seems to be BHP Billition and Rio Tinto. However, this answer needs further confirmation.
bhp
Vale is the world's largest producer of iron ore and pellets and the world's second largest diversified mining company and present in more than 30 countries.
China.
Brazil is the top producer of Iron Ore.
Mostly domestic mining operations (who are heavily subsidized) which account for something like a third to half of the world's iron ore production. They also import immense quantities from Australia and I think Brazil, as well as other iron ore exporters.
Iron ore is mined in Australia. Some of the largest iron ore deposits in the world are mind in Western Austalia, in the Pilbara region.
Australia's major mineral export is iron ore, which has consistently been the country's largest commodity export by value. The nation is one of the world's leading producers and exporters of iron ore, primarily supplying markets in China. Other significant mineral exports include coal, gold, and aluminum, but iron ore remains the dominant player in Australia's mining sector.
The countries that produce major iron ore in the world include China, Brazil, Australia, India, Russia, Canada and US. The type of iron ore found in these countries varies from each other. This factor forces or compels countries to import that kind of iron ore which is not found or is short in their country. Likewise they export the type of iron ore which is surplus one.
Iron ore is mined in many places around the world. South America, Australia, and Asia have some of the largest iron ore mines.
Minnesota is known to have the largest iron ore deposits in the United States, particularly in the Mesabi Iron Range. The state's iron ore is mainly used in steel production.
The country currently producing the most iron ore is China, which produced 900,000 tonnes of ore in 2010, over twice as much as Australia, which was second place with 420,000 tonnes. China is also the world's largest consumer of ore.