Mining is an expensive business, which is why you want as much information as possible about potential mineral deposits before you start drilling. Usually, that means conducting a geochemical soil analysis, but University of British Columbia researchers recently showed analysing soil microbe DNA may be a more accurate tool for some deposits.
They identified diamond-bearing kimberlite deposits by testing the DNA of microbes in the surface soil in what the team believes is the first use of modern sequencing of microbe DNA in the search for buried minerals.
The team tested the surface soil at an exploration site in the Northwest Territories where kimberlite had previously been confirmed through drilling. They found 59 of the 65 telltale microbes in the soil, with 19 present in high numbers directly above the buried ore. They also identified new indicator microbes to add to their set.
“The goal of this work is to develop a database,” says co-author Bianca Iulianella Phillips, a doctoral candidate at UBC’s department of earth, ocean and atmospheric sciences.
When ore interacts with soil, it changes the communities of microbes. The researchers tested this in the lab, introducing kimberlite to soil microbes and watching how they changed in number and species.
By identifying those microbes associated with kimberlite, combined with drilling, they were able to accurately map the shape of known deposits up to 160 metres below the surface.
“One deposit was pie-shaped and another was worm-shaped,” says Phillips.
In fact, the microbes returned more accurate results than geochemical analysis.
While the mechanism by which microbial communities respond to mineral deposits is uncertain, it’s unlikely to be connected to soil chemistry. Otherwise microbes and geochemistry would yield similar results.
Phillips suspects soil microbe communities instead change in relation to gases released by ores as they weather deep down in the soil.
“Rocks at depth change as a result of reactions between the host rocks and the surrounding soils and water and release CO2, hydrogen and methane,” she says. “Microbes are super-sensitive and there are a lot of them. There are thousands of species in just a bit of soil.”
Rather than replacing geochemical analysis, Phillips and her team see microbe DNA analysis as an added tool for finding ore deposits.
That’s because microbes may not be as accurate in mapping metal sulphide deposits, such as iron or copper sulphides. Unlike kimberlite deposits, which have defined boundaries, metal sulphides tend to sparsely spread out over a larger area. In other words, the signal isn’t as clean.
Using microbiology to pinpoint metal deposits isn’t new. Researchers in the 1990s used spores to detect gold deposits. What’s new is the advent of inexpensive, high-throughput DNA sequencing, making this kind of analysis more accessible.
The team believes there is commercial potential and is fine-tuning the process and hopes to eventually find commercial partners.
“Currently, microbial DNA sequencing requires specific expertise and is comparable in cost to other mineral exploration techniques, but this could change with industry adoption,” senior author and geomicrobiologist Sean Crowe said in a news release.