Diamond exploration in Ontario has had several false starts since speculation about the origin of gems in glacial drift south of the Great Lakes led explorers to the province more than a century ago.
Later, when a government geologist identified a thin section of kimberlite in drill core near Kirkland Lake, the search intensified. By the 1960s — decades before the successful hunt in the Northwest Territories erupted — industry geologists were secretly looking for a diamond mine on the Precambrian Shield of northern Ontario. The first kimberlite pipes were found in the province in the 1980s.
Interest revived during the diamond exploration frenzy of the early 1990s, but several kimberlite and lamprophyre prospects were eventually abandoned as a result of spotty grades, uninspiring tonnages or poor market conditions.
The current wave of exploration has spawned two new hotspots: the James Bay lowlands, where
Just north of Wawa, several companies have found significant quantities of the gems in an unusual host rock: the ancient volcanics that characterize the region. It seems that while both public and private sector geologists were looking for and finding kimberlite pipes — the conventional diamond host — in Ontario, a potentially important source of the gems lay right beneath their grub hoes within the relatively well-explored Superior Craton.
The unique discoveries have piqued the interest of two of the world’s biggest diamond producers. Kennecott Canada Exploration, the Canadian exploration arm of Rio Tinto, recently inked a rich option agreement with
Now that the unusual rocks that host these occurrences have been fairly well-characterized and ongoing overburden stripping is exposing new bedrock, finding diamonds in the Wawa area is becoming an almost everyday occurrence.
The Wawa story began almost a decade ago, when prospector Mickey Clement discovered carat-size alluvial diamonds in the Michipicoten River while he was panning for gold. The alluvial find was followed by Sandor Surmacz’s discovery of diamonds in bedrock, originally thought to be a lamprophyre dyke, in 1995.
Since then, numerous bedrock diamond finds have been made up to 30 km north of Wawa in the volcanic host rock now informally known as “sandorite,” after Surmacz. The primary target is a cluster of volcanic complexes that have erupted through the Catfish Assemblage of the Michipicoten greenstone belt, according to Ed Walker of PetroLogic, a consultant for both Band-Ore and Pele Mountain.
Walker and others have been able to narrow the search even further by zeroing in on the extrusive portion of the complex where the diamonds appear to be concentrated. Ontario government geologists have helped guide the search for more of the diamond-bearing tuffs and breccias.
“We’ve had a lot of help from the Ministry [of Northern Development and Mines],” says Terry Nicholson, one of a trio of prospectors who submitted a sample for caustic fusion from an outcrop they discovered on what later became Band-Ore’s GQ property. “They’ve showed us what rock types to look for and taken us on numerous field trips that made all the difference.”
The diamond occurrences form the oldest known cluster of diamond-bearing alkaline volcanic complexes in the world, according to Walker. By identifying what controls diamond distribution in these specific rock types, explorers have been able to recover diamonds from 96% of the target rocks they sample, he says in a paper titled Archean diamond-bearing volcanics near Wawa, Ont., which he presented last March at the University of Western Ontario.
“All the volcanic strata carry diamonds,” says John Buckle, an experienced diamond explorer and director of
The original 63.4 kg sample that Nicholson and prospecting partners Michael Tremblay and Jack Robert took from the Band-Ore property yielded a total of 45 diamonds, of which 10 were macrodiamonds (diamonds with one dimension measuring greater than 0.5 mm). After the discovery, the prospectors sold the GQ property, a 25-sq.-km land package, to Band-Ore for $1.2 million and 2 million shares of the junior.
Subsequent exploration on the property, which had been expanded to 39 sq. km, uncovered hundreds of showings of “heterolithic breccia” containing diamonds. One of main areas, called the Engagement zone, yielded more than 12,000 micodiamonds and 340 macrodiamonds in 406 kg of sample taken from various locations along the 335-metre-long zone. Further testing revealed an implied grade of 4.8 carats per 100 tonnes.
Kennecott field crews are now completing soil sampling, prospecting and geological mapping on the GQ property and are expected to begin drilling this summer.
Just 1.5 km north of the Engagement zone, on Pele Mountain’s Festival property, the Cristal showing yielded 327 microdiamonds in 15 grab samples taken from a sequence of breccias and lapilli tuffs overlain by lapilli and ash tuffs.
De Beers followed up the original sampling with a 100-tonne sample and, based on the results, modelled a preliminary grade of 6 carats per 100 tonnes for the Cristal showing and up to 20 carats per 100 tonnes for certain individual samples. De Beers is now processing a 455-kg sample from the property while Pele Mountain takes advantage of the improved gold price to revive some of its gold projects.
Meanwhile, partners Oasis Diamond Exploration,
Oasis has spotted most of the original volcanic stratigraphy on the property, including pillow lavas and flows overlain by clastic rocks and poorly-sorted volcanic-sedimentary deposits that grade to a fine-grained crystal tuff. “It looks as though we’re dealing with a large basin, with an anticline that is probably centred along the Trans-Canada highway,” says Buckle. “We’re getting yellow cubic diamonds in the finer-grained tuffs and clear octahedrons in the more clastic material.”
Back at the spot where Sandor Surmacz made the original discovery of bedrock diamonds in 1995, the Sandor property,
Meanwhile, conventional diamond exploration focusing on kimberlites has spread to the southern edge of the Superior Craton just north of Sault Ste. Marie.
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Both Canabrava and Southern Era used results from a 105,848 line-km geophysical survey flown by the Ontario Ministry of Northern Development and Mines under the government-funded “Operation Treasure Hunt” to identify new targets and stake new areas of interest for diamond exploration.
—The author is a Toronto-based freelance writer on mining and environmental issues.
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