Scientists Go Diamond Hunting — And Find A Prehistoric Surprise

Pink diamonds are half vanity, half science.

Where are all the diamonds buried? “That’s the billion-dollar question!” Luc Doucet, geochemist at Curtin University in Australia tells Inverse. And it’s one that Doucet’s study, published Tuesday, aims to shed some light on.

Diamonds are basically carbon trapped in the Earth’s depth that is transformed by the pressure over millions of years. And while this phenomenon is common enough, for the rocks to surface intact is rare indeed. For diamonds to be within reach of humans, tectonic shifts are needed, moving stones from places of high pressure (some 150 kilometers down) to places where we can nab them. If they move too slowly through the crust, the diamonds become graphite. So they need a lift — primarily from volcanic activity.

So where does this activity occur around the world? There’s not exactly a map to tell us where we might find the most diamonds. “It is an ongoing field of research to define which regions on the planet might host those diamonds,” Doucet says; “our study is one of them.”

Diamonds from Argyle, Western Australia.

Murray Rayner

Australian For Diamond

The new study co-authored by Doucet and published in the journal Nature, takes a close look at one of the world’s most expensive gems, pink diamonds, found primarily in Argyle, Western Australia (home to 90% of the world’s pink diamonds). When a team that included Doucet sought to narrow down a geological timeline for Argyle’s formation, they concluded the diamonds surfaced by means of volcanic activity — some 1.3 billion million years ago, older than previously guessed.

By looking at radioactive elements in Argyle minerals, the study was able to determine the time of the eruption that brought a slew of diamonds to the surface. This natural, “very precise clock,” Doucet says, revealed that the pink diamonds emerged in an eruption that took place 100 million years older than previously guessed. The new 1.3 billion-year-old estimate for Argyle’s formation overlaps with the breakup of Nuna, Earth’s first supercontinent.

So can the study be applied to diamond mining — unearthing more diamond hotspots around the world? Not so fast. “One only has to look at Argyle to appreciate the fortuity involved in preserving a diamond-bearing diatreme,” the study concludes (a diatreme is another term for a volcanic even). “It was buried to >5–6 km … and exhumed to <2 km by the Early Cretaceous, to only be partly eroded and at mineable depth at the present.”

In other words, diamonds require a goldilocks environment for humans to find them.

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