Geological ‘Goldilocks zone’ could help identify metal ore deposits

As the world shifts rapidly towards renewable energy, demand is soaring for metals like copper, cobalt, tellurium and platinum. These are vital in energy technologies, from solar panels to fuel cells to wind turbines. But metal ore deposits are mostly buried out of reach, dozens of kilometres below the surface in the Earth’s mantle: the layer of rock between the crust and the core.

In certain locations, hot liquid rock called magma naturally flows up from the mantle and into the crust, bringing with it metal deposits.

Now, geologists have identified temperature-dependent ‘valves’, where metals are intermittently allowed to flow upwards.

“When magmas reach the base of the crust, the critical metals often get trapped here and cannot reach the surface if the temperature is either too hot or too cold,” explains Iain McDonald, a geochemist at Cardiff University in Wales and co-author on a paper published in Nature Communications.

“As with Goldilocks, we have discovered that if the temperature is ‘just right’ at around 1000°C, then metals like copper, gold and tellurium can escape the trap and rise up towards the surface to form ore deposits.”

The study is part of a larger international research project called From Arc Magmas to Ore Systems (FAMOS), which aims to understand how critical minerals – particularly copper – are transported to the surface by magma.

The project studies minerals from a variety of deposits, using analytical tools to look at trace elements – each of which responds to magmatic processes in subtly different ways. This analysis is coupled with high pressure and temperature experiments to improve our understanding of how magmas, fluids and metals are cycled through the Earth.

According to Jamie Wilkinson, principal investigator for the FAMOS project from the of the Natural History Museum in London: “This paper…sheds new light on magmatic processes that operate deep in the Earth’s crust but which exert a first-order control on the accessibility of critical metals for humankind.

“The results will enable more targeted mineral exploration, thus lowering the environmental footprint associated with the discovery and extraction of green metals.”

Currently, mineral exploration can be not only financially risky but environmentally destructive, often for little return. Geology now has a critical role to play in helping us source the materials for renewable technology, without further damaging the world we’re trying to save.