Pink Diamonds Erupted to Earth’s Surface after Early Supercontinent’s Breakup

Western Australia’s Argyle mine was among nature’s preeminent treasure troves for nearly 40 years. At its peak, Argyle produced more coloured diamonds than anywhere else on Earth and earned an especially sparkling reputation for its unparalleled cache of pink diamonds.

Researchers have spent decades trying to unravel the origins of Argyle’s glimmering gems. Now, by dating minerals in the mine’s volcanic rock, scientists think they may have finally pieced together the process that created the deposit around 1.3 billion years ago. In a paper published on Tuesday in Nature Communications, the team posits that the breakup of an early supercontinent lifted Argyle’s salmon-coloured stones from crushing depths toward Earth’s surface.

Located 2,200 kilometers northeast of Perth, Australia, in the country’s rugged Kimberley region, Argyle mine once covered an area the size of 94 football fields. Between its opening in 1983 and closure in 2020, when mining the gems there was no longer economically viable, Argyle produced more than 865 million carats of rough diamonds. Most of these stones come in pale shades of yellow or brown. But a small percentage of the site’s diamonds radiate rich pinks, purples or reds. More than 90 percent of the world’s pink diamond supply including the nearly 13 carat Pink Jubilee has come from Argyle.

The pink hue of Argyle’s most lavish diamonds is linked to damage they underwent deep within the earth. According to Hugo Olierook, a geologist at Curtin University in Perth and lead author of the new study, these diamonds start out colourless. But immense tectonic pressure from colliding continents can alter the stones’ crystal structure, unlocking the potential colours hidden within. “The diamonds are being forced to bend and twist,” Olierook says. “If they’re twisted just a little bit, it will turn some of these diamonds pink.” Further twisting makes them become brown.

Argyle’s diamonds took on their pink and brown tints around 1.8 billion years ago, when a piece of what is now western Australia smashed into the northern Australian plate and warped the region’s rock. But this only explains part of Argyle’s origin story. When the continents collided, the area’s diamonds were buried in the mantle, hundreds of kilometers below Earth’s surface. If the crystals had been closer to the surface, their carbon atoms would have been compressed into a different structure, transforming them from shimmering diamonds to lumps of dark gray graphite.

A volcano was necessary to bring the molten diamonds up from our planet’s mantle. “You need some sort of tectonic trigger to bring them up to the surface,” Olierook says. As the melt rises, carbon dioxide and steam expand, sparking an eruption that he compares to popping a champagne cork. At Argyle, this eruption likely occurred at a beach, where sand and seawater interacted with volcanic rock called lamproite.

To determine when the eruption occurred, the team sliced two thin sections of Argyle’s volcanic rock and polished them down to a minuscule width. Analyzing the sample’s mineral makeup under a microscope, the researchers were able to pinpoint sand grains from Argyle’s ancient beach and to date them with the help of radioactive elements they contained. By dating the youngest sand grains, the scientists were able to estimate when the beach was buried in lava. They also used tiny lasers to determine the ages of titanite minerals, which formed in the rock when the magma melded with quartz in the beach sand.

Comparing the ages of the youngest sand grains and the oldest titanite crystals allowed the researchers to estimate that the eruption at Argyle occurred between 1.3 billion and 1.26 billion years ago. This age range was older than previous estimates, which surprised Olierook and his colleagues. “We had a betting pool going, and nobody got 1,300 million years,” he says. “That was one of those glass shattering moments.”

That eruption timing corresponds to a volatile period in Earth’s tectonic history when one of the first supercontinents, called Nuna, was splintering apart. The team posits that this instability may have reopened a seam along the continental boundary where Argyle is now situated. This in turn sparked the volcanic activity that brought the diamond-bearing melt toward the surface, creating Argyle’s expansive diamond deposits.

The new time estimates add crucial context for understanding the volcanic eruption at Argyle, says Evan Smith, a researcher at the Gemological Institute of America, who researches the geology of diamonds but was not involved in the new study. “The previous age constraint for Argyle was younger, and it was a lot less clear how to frame the eruption in a broader geological context,” Smith says. He thinks the new study adds exciting evidence that these “eruptions are related to bigger processes that affect whole continents rather than being isolated, random burps of magma.”

Olierook thinks similar events may have occurred at other continental boundaries around the world. Most diamond-bearing deposits are found in the middle of continental plates where rock is exposed. This makes Argyle an outlier. When the mine was first discovered, most geologists thought that searching for diamonds along continental plate boundaries which are often uplifted by ancient mountain belts and buried beneath soil and sand was futile.

Though gem mining in these regions remains difficult, Olierook believes there are plenty of diamonds to be found in the rough. “I think all of them will host some sort of coloured diamonds,” he says. “They may all be brown, but with a little bit of luck, there could be a few pinks in there.”

Source: Jack Tamisiea Scientificamerican

WA cuts diamond royalty rate

WA rough diamond

Western Australia has reduced its diamond royalty rate by a significant 33.3 per cent, a move that has been welcomed by Gibb River Diamonds.

The company’s lobbying has led to the reduction of the state diamond gross royalty rate from 7.5 per cent to 5 per cent.

Gibb River stated that the royalty change was in line with the recommendations of the Mineral Royalty Rate Analysis report.

This was published by the Western Australian Department of State Development and Department of Mines and Petroleum in 2015.

“The board of (Gibb River) believes that the reduction of the diamond royalty will have a very positive effect on the sector and is an extremely helpful step in further (Gibb River’s) aim of becoming a profitable diamond producer in Western Australia,” the company stated in an ASX announcement.

The rate is comparable to the 5 per cent royalty rate applied to Rio Tinto’s Argyle diamond project in Western Australia as of May this year, which was amended from the 7.5 per cent rate in 2006 when Rio Tinto decided to proceed with underground mining.

Gibb River operates the Ellendale diamond project in the West Kimberley, which supplies over 50 per cent of the world’s fancy yellow diamonds every year.

The rare colour had driven United States jeweller Tiffany & Co to ink a six-year deal with Ellendale’s former operator, Kimberley Diamonds, for the supply of the diamonds in the past.

Source: australianmining

Ellendale revival on the horizon with increased diamond value

Ellendale diamonds

Gibb River Diamonds has completed a review of the mothballed Ellendale diamond mine in Western Australia that will help it edge closer to a proposed restart.

The independent appraisal, which was completed by which was completed by Independent Diamond Valuers International (IDVI) valued gems from the Ellendale 9 East Lobe at $US750 ($1120) per carat.

This price represents a 20 per cent increase since 2008, largely due to the high number of fancy yellow diamonds unearthed at the West Kimberley-based mine.

With these results, a mine revival is looking ominous for the site, which was closed in 2015.

Last December, Gibb River Diamonds accepted an offer from the Western Australian Government apply for new tenements at the site.

“This review is important as it helps Gibb River Diamonds to make commercial decisions regarding mine planning and development priorities at Ellendale,” the company stated.

“Previous operators had a contract to sell the fancy yellow component of their production to Laurelton Diamonds (the jeweller Tiffany & Co).

“It is uncertain if similar premium prices can be achieved with any future fancy yellow goods.

“However, there is a potential opportunity to capitalise in the uniqueness of these fancy yellow goods to sell above market prices.”

The independent appraisal showed a further 18 per cent increase at the Ellendale 9 deposit to $US559 per carat since 2008.

The Ellendale 4 deposit also experienced an increase in value to $US135 per carat, representing a 5 per cent rise in 12 years.

IDVI uncovered 16 per cent fancy yellow diamonds within the Ellendale East Lobe, compared with 9 per cent in the West Lobe.

Gibb River has affirmed that as this information is based on generic sales data, future sales results could “vary significantly” from those in the report, as no sales have occurred since 2015.


POZ Minerals to Bid for Ellendale Mine

POZ Blina yellow diamonds

Only a year ago, very few in the diamond industry would have heard of POZ Minerals. But the company, better known as a phosphates producer, is trying to build a portfolio of projects in Western Australia that could make it a niche supplier of fancy-yellow diamonds.

POZ announced Tuesday that it was bidding for the Ellendale mine after the state government’s call for investors in the asset last week. While POZ already owns the adjacent Blina mine, it hopes to combine the two assets and solidify its position in the fancy-yellow category, Jim Richards, POZ chairman, explained in an interview with Rapaport News Monday.

Owning both “would result in economies of scale and efficiencies in exploration and development and would be a major step towards building a branded diamond-mining company producing the fancy yellows for which Blina and Ellendale are justifiably famous,” the company added in a statement it released Tuesday.

Richards believes the company is a front-runner in the Ellendale bid, given that it already has four mining leases at Blina and since POZ is the only miner in the area with such a license. It also already has a deal with Bunuba Group, the native titleholder for both the Blina and Ellendale land.

Ellendale comes with some history, however, after former owner Kimberley Diamonds ran up bills and a list of creditors that forced it to close the mine in 2015. That, despite a lucrative supply agreement with luxury jewelry Tiffany & Co. for its fancy-yellow diamonds.

Richards is hoping to reestablish that partnership and forge new ones with other retailers. Ellendale’s yellows have a consistency few other mines can achieve, he explains. Meanwhile, POZ is in talks with retailers in Australia and abroad for similar offtake agreements and branding of yellow diamonds from the Blina mine.

POZ is still in a testing phase at Blina and is looking for investors, or to partner with “an experienced mining company,” before production can proceed. Testing shows that fancy yellows account for about 7% of Blina’s production, while white stones make up 18%, 46% are off-white diamonds, and 29% brown. Of those, 93% are gem content or near-gem content, Richards noted.

A parcel of stones from the mine was valued at an average price of $389 per carat, with the fancy-yellow diamonds estimated at approximately $3,391 per carat.

Image: Blina mine yellow diamonds. Credit: POZ Minerals


Yellow diamond yielding mine back on the market

Fancy Vivid Yellow Diamonds

The Liquidated Ellendale mine in Western Australia, known for its fancy yellow diamonds is back on the market.

The Ellendale mine claimed to have yielded around half of the world’s supply of rare yellow diamonds during peak production.

Ellendale mine is located 120km east of Derby was also the main supplier of fancy yellow diamonds for luxury jewelry retailer Tiffany & Co.