UBC Reports | Vol. 51 | No. 1 | Jan. 10, 2005

Turning Gold into Green with Old Mine Tailings

Waste rock may help slow global warming, says geochemist

By Michelle Cook

Long considered an eyesore and an environmental problem, mine tailings -- the waste rock produced in the mining process -- may actually be helping to slow global warming by absorbing the greenhouse gases thought to cause climate change.

Greg Dipple, an associate professor of earth and ocean sciences, has been studying the waste rocks’ ability to soak up carbon dioxide (CO2) and hold, or sequester, it for long periods. His findings could impact mining operations worldwide.

Dipple first saw the phenomenon during a joint project in southern Quebec with Laval University. Working at decommissioned mines in Cassiar, northern B.C., and Clinton Creek, Yukon, for the past two summers, Dipple and his research team documented how the tailings -- the crushed rock left over after the profitable ore has been extracted -- suck CO2 from the atmosphere.

“It was pretty exciting to see this. This is something that occurs naturally on geologic timescales,” Dipple says. “We found that it happens quite quickly in mine tailings. We didn’t expect that.”

The effect is very similar to chemical weathering he explains, and occurs in tailings rich in magnesium silicate -- such as those derived from nickel, diamond, chrysolite, platinum group elements and some types of gold mines.

In a natural process called mineral carbonation, CO2 carried in rainwater reacts with silicate minerals on the surface of the tailings. The reaction binds CO2 in a solid form to the rock where it can remain in a benign state for thousands of years.

Human activity releases about eight billion tons of CO2 annually. With 500 million tons of waste rock in southern Quebec alone, Dipple thinks their potential as a CO2 sink is significant.

“With tweaking, the tailings could soak up all the greenhouse gases that mining operations produce. I think it’s possible that we could turn large mining projects into a greenhouse gas neutral industry,” he says.

It’s also possible that mines could soak up more than they produce, earning them carbon credits -- the system being developed under the Kyoto Protocol, an international agreement aimed at reducing greenhouse gas emissions. The credits could be used to pay for mine reclamation. CO2 credit futures currently trade for about CD$1.23 / tonne at the Chicago Climate Exchange, and are predicted to increase in value to CD$10/tonne or more as the Kyoto Protocol is implemented.

Not surprisingly, mining companies have taken notice of Dipple’s research.

“They didn’t believe it at first, but now they’re starting to call,” he says.

But Dipple cautions that his findings don’t offer a simple “throw it in a hole” solution to reducing carbon dioxide emissions. The next step is to figure out how to speed up the absorption process. Although Dipple and his team were surprised at how fast the process was occurring naturally in some mine sites, at others it was hardly noticeable.

The challenge will be to model and accelerate the natural reaction between the mine tailings and CO2 at a cost that will be viable for mine owners.

“It’s unpredictable because it all comes down to money,” Dipple says. “How much money will they spend? Studies show it’s possible to get an 80 per cent reaction in 28 minutes but only by spending lots of money.”

Nonetheless, he is optimistic that industrial CO2 sequestration could be in use in mines in the near future.

“I think we’ll have substantial field tests running within five years,” Dipple predicts.

He and his research team from UBC’s Mineral Deposit Research Unit will continue their field work at an active mine in Australia in February 2005.