Treasures under the ocean floor? Seawater plays a role in the formation of gold

Understanding how gold is formed is essential 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 Brucejack gold deposit in northwestern British Columbia to study and collect ancient ore-bearing rocks. The deposit, now on land due to plate tectonic processes, was originally formed on a submarine oceanic island arc about 183 million years ago. After analyzing 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 rocks, dating from the early Jurassic period, are hosted 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 deciphered their unique chemical signatures. The finding of seawater-induced gold deposition is novel and surprising.”

Data from sour milk

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 how proteins clump together to form curds when milk is dried.

“In our new study, we found that the sodium ions in seawater are what cause the gold nanoparticles to clump together, acting like the acid in sour milk and eventually forming the gold veins,” said lead author Duncan McLeish, a postdoctoral researcher in McGill’s Department. 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 good for gold formation, according to research published in Proceedings of the National Academy of Sciences.

The oceans promise to extract gold

Gold has long been a precious metal and is now also considered a critical mineral, thanks to its applications in green energy technologies, electronics, medical devices and various other fields. Land-based mining often produces low-grade ore that requires extensive processing, with significant environmental costs. The discovery of high-grade deposits in the deep ocean could help reduce the environmental footprint of gold mining, researchers said.

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