New study pinpoints critical metal accumulation around edges of ancient continental cores.

In a groundbreaking study, researchers from Macquarie University have uncovered an ancient, hidden network of geological formations like "metal highways" beneath the Earth's ancient continental cores. Shaped over millions of years, these geological formations serve as corridors for deposits of critical metals such as cobalt, copper, and rare earth elements. The discovery provides a new understanding of how these in-demand resources for the green energy transition have accumulated and offers valuable insights for more accurate exploration of untapped reserves.

Macquarie University

A new study published by a research team led by Chunfei Chen identifies the margins of ancient continental cores as promising locations for metal deposits and explains the geological mechanisms behind their formation.

The research team has demonstrated that critical metals accumulate around the edges of ancient continental cores due to silica loss in rising carbonate-rich melts. This discovery reveals new markers to facilitate more accurate exploration targets for minerals essential for supporting electrification and an overall green economy.

Transitioning from burning fossil fuels to renewable energy in a green economy requires significantly more metals, from basics like copper and nickel to more exotic minerals like lithium. The demand is such that current supplies can't keep up, and the Western drive to build a domestic battery materials supply chain increases the need for swift, accurate resource detection. To address this shortage, it is essential to discover new metal resources formed through different geological processes in previously unexplored regions.

A study published by the Earth Evolution research team at Macquarie University offers a better standing of where and how critical metals are likely to accumulate and explains the geological mechanisms behind their formation.

Sediment-dominated basins, whose size makes them attractive exploration targets, are by far the largest global source of zinc and lead.

"However, they are difficult to find as they are rarer than other zinc-lead deposits such as volcanic-hosted massive sulfide (VHMS) deposits," the Macquarie researcher wrote. "Despite their attractiveness, very few major sediment-hosted zinc-lead deposits have been discovered in the past two decades. One possible reason has been a poor understanding of fundamental, large-scale controls on mineralization."

Given that hundreds of sedimentary basins exist in the world, the key focus of the study was to find more accurate ways to screen the mineral prospectivity of various basins and pinpoint the best places to explore.

"These cores are the thickest, bowl-shaped, parts of tectonic plates. Melts that form below their centers will flow upwards and outwards towards the edges, so that volcanic activity is common around their edges," said Chunfei Chen, who led the team in its discoveries during his postdoctoral work with the Earth Evolution research group at Macquarie University

The role of carbonate-rich melts

A "carbonate-rich melt" refers to a molten rock composition within the Earth's mantle composed of a high percentage of carbon-based compounds like calcium carbonate and magnesium carbonate, playing a significant role in the deep carbon cycle by transporting carbon from the mantle to the crust.

Previous experiments by the research group demonstrated that rock melts at a depth of around 200 kilometers (125 miles) are rich in carbonate but contain much less silica. New experiments overseen by Chen show that these melts lose silica and become almost pure carbonate as they flow upwards and outwards beneath the continental cores.

"The initial melts can carry lots of critical metals and sulfur, but our new results show that these are dropped by the melt as it loses silica," said Stephen Foley, a professor at Macquarie's School of Natural Sciences. "This causes concentrations of critical metals and sulfur in linear arrangements around the edges of thick continental cores."

This validates recent observations by researchers at the Australian National University and Geoscience Australia, who found critical metals accumulated around the edges of continent cores, flagging these areas for new interest and future exploration.

By understanding the geological processes responsible for these long highways of once-molten metal and mineral accumulation, exploration efforts can zero in on areas with the highest potential yield with minimal environmental disruption.