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Carbon Dioxide Gas Reaction Fuels 'Diamond Taxis': UBC Volcanologist


January 19, 2012

Diamonds may be a girl's best friend, but diamond miners may have a fairly simple chemical reaction to thank for much of their industry’s success.

Geologists have long known that diamonds are often embedded and transported upward to the Earth's surface by molten kimberlites.

But kimberlites are dense, large rocks, and the question of how they erupt to the surface--sometimes in a matter of days or hours from depths as great as 120 kilometres--has been a mystery.

According to new findings published in the journal Nature by UBC volcanologist Kelly Russell, the abrupt arrival of diamonds on the Earth's surface may be in part driven by carbon dioxide oozing from the magma surrounding the gems as they are transported upward.

In lab experiments, Russell and colleagues sprinkled a silica-rich mineral called orthopyroxene onto a molten, carbonate-rich rock designed to mimic kimberlites. The two substances reacted and began bubbling carbon dioxide in 20 minutes.

In practice, as magma rises it may dissolve much of the rock containing orthopyroxene that it encounters, generating the same reaction underground. The gas helps speed the kimberlite--and any diamonds it may contain--to the surface. The molten material would encounter more and more rocks containing silica as it nears the surface, and accelerate.

Russel told PostMedia News that the findings may eventually help miners refine the search for diamonds, which are found in geological structures called kimberlite pipes. The pipes, which can measure up to 150 metres across and 800 metres deep, form when the foaming magma blows through the Earth's crust.

His team is now working to see how quickly orthopyroxene dissolves in the magma to better estimate how quickly the kimberlites rise.



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