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Understanding how gold is formed is critical to knowing where to find it and how to extract it sustainably. McGill researchers have answered a long-standing question in geology that could lead to new ore discoveries.

Researchers traveled to the remote Brusjack gold deposit in northwestern British Columbia to study and collect ancient ore-bearing rocks. The deposit, now on land due to plate tectonic processes, originally formed in an underwater oceanic island arc about 183 million years ago. After analyzing the samples at McGill and the University of Alberta, they discovered that seawater had mixed with ore fluids in the Earth’s crust to form gold.

“These Early Jurassic rocks are found in volcanic and sedimentary formations,” said co-author Anthony Williams-Jones, Logan Professor of Geology and Geochemistry in McGill’s Department of Earth and Planetary Sciences. “Using high-resolution mass spectrometry, we decoded their unique chemical signatures. The discovery of seawater-induced gold deposition is novel and surprising.”

Clues from yogurt

The findings build on the McGill team’s 2021 discovery that gold nanoparticles combine to form high-quality gold deposits, in a process similar to the way proteins clump together to form curds when milk sours.

“In our new study, we found that the sodium ions in the seawater are what cause the gold nanoparticles to stick together, acting like the acid in yogurt and ultimately forming gold veins,” said lead author Duncan McLeish, a postdoctoral researcher at McGill Department of Earth and Planetary Sciences.

The presence of seawater suggests that gold veins may form on the seabed. This means untapped gold resources may exist in underwater island arcs and deep ocean trenches where conditions are excellent for gold formation, according to research published in Proceedings of the National Academy of Sciences.

The oceans are promising for gold mining

Gold has long been a precious metal and is now also considered a critical mineral, thanks to its applications in green energy technologies, electronic devices, medical equipment and various other fields. Surface mines often produce low-grade ore that requires intensive processing with significant environmental costs. Finding high-quality deposits in the ocean depths could help reduce the environmental footprint of gold mining, scientists said.

“Our findings suggest that it may be easier to form the rare but impressive concentrations of gold found in high-grade gold veins in submarine settings. “With the recent interest in mining undersea mineral deposits, our research suggests that Earth’s oceanic crust may indeed contain resources, many of which are necessary for the green energy transition, at a level never before appreciated,” said Williams- Jones.