The Kidd mine began operations in 1966 as an open pit mine after assays indicated an ore body 800 feet long, 300 feet wide, and a vertical depth of 800 feet with copper, Zinc, and silver. The operation eventually evolved into an underground mine.
The Kidd deposit is one of the largest volcanogenic massive sulfide ore deposits in the world, and one of the world’s largest base metal deposits. But what is interesting about the mine is what lies beneath the 10,000 feet deep surface.
Below the Earth’s surface is a literal maze of tunnels and shafts plunging 2.4 kilometers (1.5 miles) – to an extreme depth of the mine – which at 3.1 kilometers (1.9 miles). The shafts are so deep that a huge ventilation system is needed, otherwise, the temperature would be 34 °C (93 °F).
The search for water beneath the Earth
But we’re not going to talk about the ore produced by the mine or even the open pit. It is what was found beneath the surface that is so fascinating to hydrologists, scientists, and geologists. Barbara Sherwood Lollar, a geochemist at the University of Toronto has been on a search for pools of water deep within the tunnels.
“You get into a small truck or vehicle and go down a long, winding roadway that corkscrews down into the Earth,” she tells The Scientist. At the deepest point under the surface, she says “we are literally walking along what was the ocean floor 2.7 billion years ago, It’s an utterly fascinating and magical place to visit.”
In 2013 they found water dating back about 1.5 billion years at the Kidd Mine, but searching deeper, scientists found an even older source buried underground. This initial discovery of the ancient liquid in 2013 came at a depth of around 2.4 kilometers (1.5 miles) in an underground tunnel in the mine.
“[The 2013 find] really pushed back our understanding of how old flowing water could be and so it really drove us to explore further,” Loller told The BBC in 2016. “And we took advantage of the fact that the mine is continuing to explore deeper and deeper into the earth.”
And another source of water was found at about 3 kilometers (1.9 miles) down, and according to Sherwood Lollar, there’s a lot more of it than you might expect. “When people think about this water they assume it must be some tiny amount of water trapped within the rock,” she said.
Samples were taken back to the University of Toronto and tested for gases that had been dissolved in the ancient pool of water. They found traces of helium, argon, and neon and this enabled them to date the water. At two billion years old, it’s the oldest water found in the history of the world.
“But in fact, it’s very much bubbling right up out at you. These things are flowing at rates of liters per minute – the volume of the water is much larger than anyone anticipated,” said Loller. However, this water is not the kind you would drink. It is salty. “These are waters that have been in contact with the rock for long geochemical timescales—they’re full of dissolved cations and anions that they’ve leached out of the minerals.”
And this water has a distinct “musty odor.” Loller says that as she and her colleagues walk along the tunnels, if they get a whiff of that stenchy smell, they know to follow their noses to the source. And where there is water, there is a potential for life.
The search for life in a pool of water
In 2006, Loller was part of a team led by Tullis Onstott at Princeton University that discovered an anaerobic, sulfate-reducing bacterium thriving in the sulfate-rich fracture waters of Mponeng gold mine in South Africa, 2.8 kilometers (1.9 miles) underground.
Another group described a diverse microbial community living at a similar depth in the Earth’s crust, accessed via a borehole drilled into the ground in Finland. Now, with the recent discovery of hydrogen- and sulfate-rich water seeping out of the rock in Kidd Mine, Loller and her team are hoping to find life again.
The location of the Kidd mine lies within the Precambrian Canadian Shield. Researchers observed a unique distribution pattern called sulfur isotope mass-independent fractionation in the water they analyzed. This signature is thought to be produced by photochemical reactions in early Earth’s atmosphere prior to the Great Oxidation Event 2.4 billion years ago.
Long Li, an assistant professor at the University of Alberta’s Department of Earth and Atmospheric Sciences explains: “The sulfate in this ancient water is not modern sulfate from surface water flowing down. What we’ve found is that the sulfate, like the hydrogen, is actually produced in place by reaction between the water and rock. What this means is that the reaction will occur naturally and can persist for as long as the water and rock are in contact, potentially billions of years.”
What does this all mean? Well, the billion-year-old rocks on the surface of Mars are similar to the mineral assemblage in the studied area in northern Ontario.
Li says, “Because this is a fairly common geological setting in early Earth as well as modern Mars, we think that as long as the right minerals and water are present, likely kilometers below the surface, they can produce the necessary energy source to support the microbes. I’m not saying that these microbes definitively exist, but the conditions are right to support microbial life on Mars.”
The Kidd mine is nearing the end of its active life and is due to be closed in 2020. It is not known if scientists will be able to continue their research. And just so everyone knows – Visiting the Kidd mine is forbidden. It is a restricted area and only staff members and those with special permission are allowed on site.
