The Argyle Mine in Western Australia has been amongst nature’s excellent treasures for almost 40 years. At its peak, Argyle produced extra coloured diamonds than wherever else on Earth and gained a very glowing fame for its unmatched cache of pink diamonds.
Researchers have spent many years making an attempt to unravel the origins of Argyle’s glowing gems. Now, by relationship minerals discovered within the mine’s volcanic rocks, scientists consider they might have lastly pieced collectively the method that created the deposits about 1.3 billion years in the past. In a paper revealed on Tuesday in Nature CommunicationsThe staff assumes that The breakup of an early supercontinent lifted salmon-colored argyle rocks from the overwhelming depths toward the Earth’s surface..
Positioned 2,200 kilometers northeast of Perth, Australia, within the nation’s rugged Kimberley area, the Argyle mine coated an space equal to 94 soccer fields. Between its opening in 1983 and its closure in 2020, when gemstone mining there was now not economically viable, Argyle produced greater than 865 million carats of tough diamonds. Most of those stones are available pale shades of yellow or brown. However a small proportion of the positioning’s diamonds radiate wealthy pink, purple or crimson colours. Greater than 90 % of the world’s provide is pink diamonds, together with roughly 13 carats Pink Jubilee-He got here from Argyll.
The pink shade of Argyle’s most luxurious diamonds is linked to the injury they’ve suffered deep throughout the earth. In accordance with Hugo Ollerock, a geologist at Curtin College in Perth and lead writer of the brand new examine, these diamonds begin out colorless. However huge tectonic strain ensuing from the collision of continents can change the crystalline construction of the stones, revealing the potential colours hidden inside. “Diamonds are compelled to bend and twist,” Ollerok says. “In the event that they have been a little bit crooked, a few of these diamonds would flip pink.” Additional twisting makes it flip brown.
Argyle diamonds acquired their pink-brown shade about 1.8 billion years in the past, when a bit of what’s now often known as Western Australia collided with the northern Australian plate and distorted the rocks of the area. However this solely explains a part of Argyle’s origin story. When the continents collided, the diamonds discovered within the space have been buried within the mantle, a whole lot of kilometers beneath the Earth’s floor. If the crystals have been nearer to the floor, their carbon atoms would have been compressed to type a distinct construction, turning them from glowing diamonds into lots of darkish grey graphite.
The volcano was essential to eject molten diamonds from our planet’s mantle. “You want some form of tectonic catalyst to boost it to the floor,” Ollerok says. Because the melting level rises, carbon dioxide and steam develop, leading to a volcanic explosion just like popping the cork of a champagne bottle. At Argyle, this eruption probably occurred on the seaside, the place sand and seawater interacted with volcanic rocks referred to as lamproite.
To find out when the eruption occurred, the staff reduce two skinny sections of Argyle’s volcanic rock and polished them to a tiny width. By analyzing the mineral composition of the pattern below a microscope, the researchers have been capable of determine sand grains from historic Argyle Seaside and date them with the assistance of the radioactive parts they comprise. By relationship the smallest grains of sand, scientists have been capable of estimate when the seaside was buried in lava. In addition they used small lasers to find out the ages of titanium minerals, which fashioned within the rock when magma merged with quartz in seaside sand.
Evaluating the ages of the youngest grains of sand and the oldest titanium crystals allowed the researchers to estimate that the volcanic eruption at Argyle occurred between 1.3 billion and 1.26 billion years in the past. This age vary was bigger than earlier estimates, which shocked Ollerok and his colleagues. “We had a betting pool going, and nobody bought 1,300 (million years),” he says. “That was a type of glass-shattering moments.”
The timing of the eruption corresponds to a unstable interval in Earth’s tectonic historical past when one of many first supercontinents, referred to as Nuna, was splitting aside. The staff hypothesizes that this instability could have reopened a seam alongside the continental boundary the place Argyle now lies. This in flip sparked volcanic exercise that melted the diamonds towards the floor, creating the in depth diamond deposits at Argyle.
The brand new time estimates add essential context for understanding the Argyle volcanic eruption, says Evan Smith, a researcher on the Gemological Institute of America, who researches the geology of diamonds however was not concerned within the new examine. “The earlier age restriction for Argyle was youthful, and it was a lot much less clear tips on how to body the eruption in a broader geological context,” Smith says. He believes the brand new examine provides thrilling proof that these “volcanic eruptions are linked to bigger processes affecting complete continents reasonably than being remoted, random burps of magma.”
Olerock believes comparable occasions could have occurred on different continental borders around the globe. Most diamond-bearing deposits are discovered in the midst of continental plates the place rocks are uncovered. This makes Argyle an excessive case. When the mine was first found, most geologists believed that trying to find diamonds alongside continental plate boundaries—which are sometimes uplifted by historic mountain belts and buried beneath soil and sand—was futile.
Though extracting gems in these areas continues to be troublesome, Olleruk believes there are many diamonds to be discovered within the tough. “I feel they may all host some form of coloured diamonds,” he says. “They might be all brown, however with a little bit luck, there generally is a little little bit of pink in them.”