The geology behind Ontario’s world class metal districts – by Lesley Stokes (Northern Miner – September 14, 2016)

VANCOUVER — Ontario has a long and lively geological past dating back 3.3 billion years, when the Earth was covered by oceans. During that time, intense volcanism formed the Earth’s crust, giving way to a barren and lifeless landscape blasted by radiation from the sun.

Three billion years ago, plate tectonics moved thin rafts of rocks at a rate much faster than they do today. Over time, the volcanic islands butted together into one large block of land, with most of the action starting around the Red Lake area, a prolific gold-mining camp in northwest Ontario.

As the volcanic terranes collided, balls of magma were injected into the volcanic pile, which cooled into enormous granitic batholiths. During the deformation and magmatism, the rocks were baked and transformed into what’s known as “greenstone belts,” which are excellent hosts for orogenic, high-grade gold deposits, along with volcanogenic massive sulphides (VMS), magmatic nickel-copper, platinum group metals (PGMs) and chromium deposits.

Today, greenstone belts such as the “Abitibi” which spans the Ontario-Quebec border, make up the southern part of a much larger craton in Canada called the “Superior.” The Abitibi is one of the largest greenstone belts in the world, with gold production exceeding both the Kalgoorlie camps in Western Australia, and the Homestake deposits in South Dakota.

Ontario’s portion of the Abitibi hosts world-class gold camps, including Timmins, Kirkland Lake, and Larder Lake. Quebec’s portion of the Abitibi includes the Val-d’Or, Malartic and Rouyn-Noranda camps. Gold production from the Abitibi tops 170 million oz., with mining dating back to 1901.

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