Geology Matters: Ontario farmer uses mining background to identify better soils

  • John Slack at Spanish River Carbonatite Complex

John Slack at Spanish River Carbonatite Complex

Educated at the Haileybury School of Mines, John Slack is a Canadian mining technologist-turned-farmer who uses his thorough understanding of geology to promote remineralization and sustainable soil fertility.

John Slack's Calabogie Farm

John Slack’s Calabogie Farm

“Promoting the use of rock dust — and the throwing away of your fertilizer bag — has been a really tough row to hoe, but we’re now going to see major breakthroughs, particularly as we move to a ‘greener’ environment, where people are thinking about this more,” he said. “The fact of the matter is it does work.”

Slack began his professional life employed with a progressive mineral exploration company in the Yukon Territory and British Columbia, analyzing soil geochemistry. From there, he moved back to his home province of Ontario and used his skills to locate economic mineral deposits, forming a small company with his father — a mining engineer.

“During that time, my father purchased a farm. And so, when I had time off, I came back and would help him on the farm, and I just fell madly in love with farming.”

In the late 1980s, the mining exploration industry collapsed, which provided Slack with an opportunity to switch careers. He decided to move to the family farm in Southern Ontario and take up agriculture. Rather than abandon his geological background, though, he used it to identify unique mineral deposits across Central Canada that would work for direct application for certified organic food production.

Diagram showing the geological features of the Spanish River Carbonatite Complex

Spanish River Carbonatite Complex (Click to enlarge)

“What we found is we knew more about the rocks and alternatives being sold to farmers that were certified organic than the people who were selling the rocks, because this was our world — the world of geology and mineralogy.”

He added: “We discovered a deposit that had already been identified, and it was referred to as the ‘Spanish River Carbonatite Complex.’ Carbonatites are very unique, because they’re igneous in origin, or magmatic in origin, but they are predominantly calcium carbonate, which is highly unusual. Fortuitously, [the deposit] has high levels of phosphorus and potassium, and some very unique trace element signatures.”

From a geological perspective, Slack has championed a variety of practical concepts that are rarely, if ever, considered in the farming industry — mineral reactivity, microbial mineral interaction, and rock dust remineralization. This self-taught farmer said he is “very much in tune” with soil regeneration through grass production. “I brought forth a brand-new mineral dynamic at one time in agriculture, which has sort of culminated into my kind of being an expert.”

He added: “Through the ‘90s, we explored and ran trials on our farm. In the early 2000s, we licensed a quarry, and I ended up selling rock dust throughout Ontario and into the U.S., up until about five years ago.”

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New farm, new soils

After several years farming on the outskirts of the Greater Toronto Area, Slack recently relocated the family farm to Eastern Ontario, taking advantage of “outrageous land prices” for his old farm, as well as the unique, fertile mineralogy of his new one. Geologically speaking, his new farm near Calabogie has among the most interesting soils he has seen.

Sheep on Calabogie Farm

“I’m sitting on highly calcareous (meaning calcium-rich) soils, which are the best in the world, which have been smeared and intruded with a very complex group of rocks and minerals that aren’t normally found anywhere on earth, or only very rarely on earth, and very high levels of natural metals. I often state that the Ottawa Valley’s uniqueness is a direct result of this geological complexity.”

According to Slack, the area of Eastern Ontario where he now farms has been clear-cut at least three times since European settlers arrived. However, there is little evidence of previous deforestation given the diversity of trees in the region currently. “We get white pine, red pine, oak, maple, and the list goes on and on. I’ve even been told, and I have to verify it, that the highest concentrations and varieties of fungi occur in Eastern Ontario.”

What the local flora tells this former mining expert is that a minerally-complex earth aids in vegetation’s ability to recover from strife, which just highlights the potential effectiveness of soil remineralization. “It’s the absolutely unique geology and the potential that I could produce extremely unique foods.”

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Proposing an annual conference

The major flaw in agronomy education is the absolute lack of geoscience appreciation, Slack said. It might not be the “end-all and be-all,” he suggested, but it certainly is a necessary part of the complex picture. “To me, personally, I don’t think that we’re ever going to resolve rejuvenating, remineralizing and getting our soils back to where they were, unless these people who are doing it have a really sound footing in geoscience.”

With the unique mineralogical characteristics of the soils on his farm, which is located in convenient proximity to downhill skiing and quality hotels, Slack sees exceptional potential for remineralization conferences at Calabogie — an opportunity to bring subject-matter experts to a North American tourist destination able to accommodate large groups. Organizers could rent buses and conduct field trips to actual mineral deposits.

“Once we get through COVID and the world opens up again, we should put this conference on. It’s desperately needed,” he said, noting many people still doubt the power of rock dust and real-world exposure to what mineralogy can do might just turn some skeptics into believers. “If we embrace this, and get more people to embrace this, then we can truly restore the soils of this earth, which is going to result in sequestering carbon and cleaning up our oceans.”

He added: “That’s what I see as the future. If I can help to facilitate an annual event in an area that’s a prime example of how effective remineralization can work, then that’s what I’d like to do.”


Carter Haydu is a journalist and professional writer with more than 13 years of experience. Since 2012, he has written primarily on the Alberta energy sector for a Calgary-based trade publication. Much of his work has dealt with environmental issues facing the upstream oil and gas industry. In 2018, Carter attained a technical writing certificate from a reputable Canadian university. He hopes his skillset can support RTE’s sustainable initiatives.

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