The discovery, made under the Timmins mine in Ontario, is important for understanding life on Earth and Mars, researchers said.
Dr Greg Holland, of Lancaster Environment Centre at Lancaster University, along with scientists from Manchester University and two Canadian universities found pockets of water that have been isolated from the outside world for more than 1.5 billion years.
The water was discovered from crystalline rock nearly one and a half miles beneath the Earth’s surface.
The water was analysed using a dating technique which involves studying the different types of xenon, an inert gas, dissolved in the samples.
Xenon isotopes can be used to identify when a fluid was last in contact with the atmosphere at the Earth’s surface.
Using this method, the team discovered that the water is at least 1.5 billion years old, hundreds of millions of years older than samples the same team collected from a gold mine in South Africa in 2006.
This younger water contained micro-organisms that had survived on energy from dissolved hydrogen and methane, without needing sunlight.
The Canadian samples are now being analysed to determine whether such life forms are present in the water.
“Our Canadian colleagues are trying to find out if the water contains life right now,” said Holland, lead author of the study.
“What we can be sure of is that we have identified a way in which planets can create and preserve an environment friendly to microbial life for billions of years.
“This is regardless of how inhospitable the surface might be, opening up the possibility of similar environments in the subsurface of Mars,” he said.