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 mine 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, originally formed in a submarine oceanic island arc about 183 million years ago. After analyzing samples at McGill and the University of Alberta, they found 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 finding of seawater-triggered gold deposition is novel and surprising.”

Help from sour milk

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

“In our new study, we discovered that sodium ions in seawater cause the gold nanoparticles to clump together, acting like the acid in sour milk and eventually forming 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 could be forming in the seabed. This means that untapped gold resources may exist in undersea island arcs and deep ocean trenches where the conditions are best for gold formation, according to research published in Proceedings of the National Academy of Sciences.

The oceans promise to mine gold

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

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