New findings shed light on finding valuable ‘green’ metals

How concentrations of metals can be transported from deep within the Earth's interior mantle by low temperature, carbon-rich melts

MACQUARIE UNIVERSITY

Research led by Macquarie University sheds new light on how concentrations of metals used in renewable energy technologies can be transported from deep within the Earth's interior mantle by low temperature, carbon-rich melts. 

The findings published this week in the journal Science Advances may assist global efforts to find these valuable raw materials.  

An international team led by Dr Isra Ezad, a postdoctoral research fellow from Macquarie University’s School of Natural Sciences, carried out high pressure and high temperature experiments creating small amounts of molten carbonate material at conditions similar to those around 90 kilometres depth in the mantle, below the Earth’s crust. 

Their experiments showed carbonate melts can dissolve and carry a range of critical metals and compounds from surrounding rocks in the mantle – new information that will inform future metal prospecting. 

“We knew that carbonate melts carried rare earth elements, but this research goes further,” says Dr Ezad. 

“We show this molten rock containing carbon takes up sulfur in its oxidised form, while also dissolving precious and base metals – ‘green’ metals of the future – extracted from the mantle.” 

Most of the rock that lies deep in the Earth’s crust and below in the mantle is silicate in composition, like the lava that comes out of volcanoes.  

However a tiny proportion (a fraction of a percent) of these deep rocks contain small amounts of carbon and water that causes them to melt at lower temperatures than other portions of the mantle.  

These carbonate melts effectively dissolve and transport base metals (including nickel, copper and cobalt), precious metals (including gold and silver), and oxidised sulfur, distilling these metals into potential deposits.  

“Our findings suggest carbonate melts enriched in sulfur may be more widespread than previously thought, and can play an important role in concentrating metal deposits," says Dr Ezad. 

The researchers used two natural mantle compositions: a mica pyroxenite from western Uganda and a fertile spinel lherzolite from Cameroon.  

 

Thicker continental crust regions tend to form in older inland regions of continents, where they can act as a sponge, sucking up carbon and water, Dr Ezad says. 

“Carbon-sulfur melts appear to dissolve and concentrate these metals within discrete mantle regions, moving them into shallower crustal depths, where dynamic chemical processes can lead to ore deposit formation," Dr Ezad says. 

Dr Ezad says that this study indicates that tracking carbonate melts could give us a better understanding of large-scale metal redistribution and ore formation processes over Earth's history. 

“As the world transitions away from fossil fuels to battery, wind and solar technology, demand for these essential metals is skyrocketing, and it’s becoming harder to find reliable sources,” says Dr Ezad.  

“This new data provides us with a mineral exploration space previously not considered for base and precious metals – deposits from carbonate melts,” she says. 

The multi-institution team were from Macquarie University in Sydney, the University of Western Australia in Perth, University of Oxford in the UK and Australian National University, Canberra. 

END 

Incipient carbonate melting drives metal and sulfur mobilization in the mantle was published in Science Advances on 22 March 2024. DOI: 10.1126/sciadv.adk5979  

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JOURNAL

Science Advances

DOI

10.1126/sciadv.adk5979 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

New findings shed light on finding valuable ‘green’ metals

ARTICLE PUBLICATION DATE

22-Mar-2024

COI STATEMENT

All authors declare that they have no competing interests. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOR Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Authors acknowledge the facilities, and the scientific and technical assistance of Microscopy Australia and the Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, a facility funded by the University, State and Commonwealth Governments of Australia. High-resolution SEM images were created at Macquarie University. Beamtime operations were performed on GSECARS 13-IDE. Synchrotron XRF mapping and S-XANES data were collected during beam time awarded to I.S.E. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13-IDE), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR-1634415).