To know where to find gold and how to extract it in an environmentally friendly manner, it is crucial to understand how this metal forms. Researchers at McGill University have managed to answer a long-standing question geologists have had, and their findings could lead to the discovery of new deposits.
The McGill research team studies a mineralized (gold-containing) vein underground at the Brucejack Mine.
Credit: Duncan McLeish
The researchers traveled to the Brucejack gold mine in northwestern British Columbia to study very ancient mineralized rocks and gather samples. Today located on the Earth's surface due to tectonic plate activity, the deposit formed in a submarine volcanic arc around 183 million years ago. After analyzing the samples at McGill University and the University of Alberta, the researchers found that seawater had combined with mineralizing fluids in the Earth's crust to form gold.
"These rocks, dating back to the Early Jurassic period, were trapped in sedimentary and volcanic formations," explains one of the study's co-authors, Anthony Williams-Jones, Logan Chair Professor of Geology and Geochemistry in the Department of Earth and Planetary Sciences at McGill University. "Using high-resolution mass spectrometry, we succeeded in decoding their unique chemical signature. Finding gold deposits formed from seawater was novel and unexpected."
A phenomenon similar to milk curdling In 2021, the McGill team had already made a discovery providing clues to this mystery. The researchers found that gold nanoparticles combine to form high-grade gold deposits, similar to how proteins aggregate to form curds when milk sours.
"In our new study, we discovered that sodium ions present in seawater played the same role as acid in curdling milk, causing gold nanoparticles to clump together into veins," explains the study's lead author, Duncan McLeish, a postdoctoral fellow in the Department of Earth and Planetary Sciences at McGill University.
High-grade gold presence in the Brucejack Mine.
Credit: Duncan McLeish
The presence of seawater suggests that gold veins could form on the ocean floor. Undiscovered gold deposits may therefore exist in underwater volcanic arcs and ocean trenches, where conditions are ideal, according to the study published in the journal Proceedings of the National Academy of Sciences of the United States of America.
The ocean, a promising lode Long considered a precious metal, gold has become essential, as it is used in green energy technologies, electronic devices, and medical equipment. Ore extracted from terrestrial mines is often low grade and requires considerable processing, which comes with significant environmental costs. In contrast, extracting potential high-grade deposits found in the deep sea could reduce the ecological footprint of gold mining, according to the researchers.
"Our observations suggest that the seabed could facilitate the formation of rare but spectacular gold concentrations, like those we found in the high-grade veins. Underwater mining is gaining more attention. Our study hints at the possibility that the oceanic crust harbors numerous resources necessary for greening the energy sector, and in unexpected quantities," explains Prof. Williams-Jones.
References:
The article "Extreme shifts in pyrite sulfur isotope compositions reveal the path to bonanza gold," by McLeish, D. F., Williams-Jones, A. E., Clark, J. R., and Stern, R. A., was published in the journal Proceedings of the National Academy of Sciences (PNAS) in May 2024.