BY ANTHONY KING
The Yilgarn Craton stretches across south central Western Australia, and contains some of Earth’s oldest crust – including zircon crystals dating back some 4bn years, and extensive deposits of iron-rich and magnesium-rich rocks.
These may be suitable for creating hydrogen by injecting water down into iron-rich rocks to oxidise ferrous iron to ferric iron, generating the tell-tale orange hue of oxidised iron, according to researchers.
Key to this reaction is an abundance of dark igneous rocks rich in magnesium (called ultramafic) that contain up to 10% by weight of ferrous iron. The serpententisation reaction happens in nature when water reacts with ultramafic rocks to form serpentine rocks and minerals – so-called because of their green, mottled snake-like appearance – and hydrogen gas.
Other locations such as Pilbara Craton in Western Australia and Gawler Craton in South Australia could generate hydrogen, says Lingping Zeng at CSIRO, a government research agency that carried out the study (International Journal of Hydrogen Energy, DOI: 10.1016/j.ijhydene.2026.155631).
‘Both contain ancient iron-rich and magnesium-rich rocks that could potentially support similar water-rock reactions,’ he adds.
Other parts of the world also have these iron-rich mantle rocks near enough to the surface to generate hydrogen.
The necessary rock types are formed at depth, where there is little water, but can be pushed up during mountain building. Beneath the Earth is ‘a giant and undervalued hydrogen factory,’ according to a 2022 perspective co-written by geochemist Eric Gaucher (Nature Geoscience, DOI: /10.1038/s41561-022-01043-9). Roughly 20m t of hydrogen escapes from the surface towards the atmosphere each year, it noted.
Hydrogen is generated naturally when water comes into contact with iron-rich rocks such as peridotite at the right temperature and pressure. If hydrogen gas is trapped by rocks above, it could be drilled and brought to the surface. ‘We could first drill into rocks with hydrogen generated in a natural way,’ says Gaucher. ‘Then we could add water to the system to react with the rocks and generate new hydrogen.’
Gaucher’s startup firm, RockyH2 in Lyon, France, is optimising the natural production of geologic hydrogen and developing catalysts to allow water access ferrous-iron in rocks to generate orange hydrogen. His team is carrying out exploration and test drills for geologic hydrogen in Switzerland. ‘We have a big piece of mantle at a depth of around 4km north of Lausanne in the Swiss Alps,’ he explains. Rocks with the potential to generate hydrogen are present at sometimes shallower depths in the Pyrenees and Alps, as well as below Kansas, Nebraska and Iowa in the US, and in Cornwall, UK.
In Australia, Zeng and his team created a virtual underground chemical reactor to explore what happens when salty water hits iron-rich rocks. Temperature was especially important. ‘In our simulations, cumulative hydrogen generation increased by almost two orders of magnitude between 150 and 300°C,’ while low to moderate salinity and alkaline conditions encouraged hydrogen formation, Zeng explains.
His group plans more lab tests and then a field-scale demonstration. ‘The major task now is to demonstrate the reaction rates, fluid flow and economics at progressively larger scales,’ Zeng says.
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