Explainer: What is iron ore?

Cosmos Magazine


Cosmos is a quarterly science magazine. We aim to inspire curiosity in ‘The Science of Everything’ and make the world of science accessible to everyone.

By Cosmos

By Dr Erick Ramanaidou,


Grace Kirkby

Iron ore is rock rich in iron oxides (Fe2O3) and includes minerals like hematite and magnetite.

Most of the world’s iron ore is found in banded iron formations (BIFs), which occur on all continents, and in all states of Australia. Western Australia accounts for 90 per cent of Australia’s iron ore.

This rich mineral endowment is due to hardworking tiny photosynthetic bacteria many millennia ago.

BIFs are like ancient storytellers etched in stone. Although they’re on land now, their story starts in the ancient oceans.

Banded iron formations are evidence of what is called “The Great Oxidation Event.”

Iron ore and green steel

Many BIFs around the world were formed more than 3000 – 2500 million years ago. These ancient oceans had high levels of dissolved silica and iron, being washed into the oceans off the land. Then cyanobacteria  developed photosynthesis, forming colonies of stromatolites. Stromatolites can still be seen today in Shark Bay and Lake Clifton in Western Australia.

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Banded iron, tightly folded, approximately 3 billion years old. southern Pilbara region, Western Australia. (Photo by Auscape/Universal Images Group via Getty Images)

As the bacteria began photosynthesising, they started releasing oxygen into the oceans. Seasonal blooms of algae boosted the amount of oxygen in the seawater. Oxygen then reacted with the soluble iron to form insoluble iron oxide. Iron oxides fell to the ocean floors as minerals like magnetite and hematite.

These sediments continued to accumulate in alternating bands on the ocean floors for nearly a billion years. They created the banded formations or BIFs we now find. These rocks reflect millions of years of change in each layer.

Once most of the minerals in the ocean were oxidised, the oxygen was finally able to make its way out of the ocean to create our atmosphere.

Overtime continental uplifts, sea level changes and billions of years of erosion have exposed the banded iron formations on land, which we now mine.

Fast forward to today and thanks to the hard work of these tiny bacteria, we now have iron ore.

3.8 billion years ago in Greenland (Isua) we had a little blip in BIF, but the conditions weren’t right for the photosynthetic microorganisms to take off.”

Drawn from an original article on CSIRO News

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