Take a peek behind the Argyle diamond story that made global headlines

The New York Times feature on Argyle diamonds: Pink Diamonds Emerged Out of One of Earth’s Most Ancient Breakups featured octahedral pink diamonds found in the Argyle diamond mine. Photo supplied by Murray Rayner, Principal Geologist at Rio Tinto. Image: AuScope edited

100 million years changes things. A recent NCRIS enabled study out of the John de Laeter’s Centre GeoHistory Facility and Western Australian Thermochronology Hub has rewritten the history of some of the world's most famous diamonds. We sat down with Dr Hugo Olierook, lead author of the study, to talk about all things diamonds, research and deep time.

Welcome, Hugo.

Congratulations on your breakthrough research and recent award from the Australian Institute of Policy and Science - WA Tall Poppy of the Year. It's such a strange but very Australian name for an award.

Thanks for the congrats – it’s a very strange name indeed.

I’m originally from the Netherlands, so “Tall Poppy Syndrome” was completely new to me once I set foot on Aussie shores in 2007. But, the Dutch have a similar expression - “boven het maaiveld uitsteken”, which alludes to a weed or a grass that’s grown too high and deserves to be chopped down.

So, if you ever see me less-than-humble, feel free to cut me down to size!

Can you give us an overview of the media interest and impact your paper has generated?

It’s been a wild ride. Not in my wildest dreams did I think a story about re-dating diamonds would go as far and wide as it did.

We wrote an article about Argyle, the largest diamond producing mine from 1983 to 2020 and the largest supplier of pink diamonds ever, with an estimated 90% of all pink diamonds produced coming from the mine in the heart of the Kimberley region of Western Australia.

I guess the allure of pink diamonds excited and inspired the public.

Over the course of a week or so, we conducted close to thirty interviews for scientific magazines, newspapers, radio channels and local TV news.

And I say we because it would not have been possible without Denis Fougerouse and Luc Doucet, co-conspirators who helped deal with the onslaught of interviews. These boys kept me sane (more or less)!

Often, calls for interviews came from the Americas, meaning late evening or early morning interviews that, coupled with a healthy dose of nerves, meant some sleepless nights.

Still, it was worth it. A whopping 700 news outlets published our story, with some of my favourite ones in the New York Times, ABC and Scientific American.

Shortly after, the article was listed in the highlights list on Nature Communications and nominated as the top media story at Curtin for 2023. A wild ride indeed.

Watch: Hugo discussing the Argyle diamond discovery. Source: Curtin University

What was the origin of this research idea?

Pink diamonds are an enigma. We know we need carbon deep down in the Earth (if the carbon is shallow, we get graphite). And we know we need continents colliding; pink diamonds are damaged diamonds, forming from enormous pressures during continental collision, turning their original colourless lustre to pink, red and brown hues.

But why is Argyle the only place on Earth where we can find an appreciable quantity of them?

It all started with a corridor conversation two years ago between Denis Fougerouse and Curtin emeritus professor Bob Pidgeon, who did the original dating work in the mid-to-late 1980s.

Bob published an age just shy of 1200 million years ago for the eruption of the Argyle diamond pipes. But, he was never quite happy with the original age. He said so in his original research paper but also remarked upon it in the corridor.

The issue was that these volcanic pipes always need a trigger to take them from the bowels of the Earth to the surface in a matter of days. And at 1200 million years ago, there really was no plausible trigger for the Argyle volcano to erupt.

Fast forward six months, and Denis gets a phone call from Murray Rayner, Principal Geologist at Rio Tinto, who’d worked on Argyle for nearly two decades.

Murray confided that, with Argyle having closed in 2020, he wanted to preserve its legacy by offering to run a workshop for students at Curtin and the University of Western Australia, the two universities that offer geology in Perth.

Denis gladly accepted the invitation. In early 2022, Murray arrived with a wealth of Argyle memorabilia, from rocks to diamonds, and a story that tied it together. But still, there was that nagging feeling that the age of diamond emplacement was not quite right.

After having seen the rocks first-hand, and knowing that this was an unresolved conundrum, Denis approached Luc and myself to try and nut out a solution once and for all.

Hand sample (~15 cm wide) of the Argyle rock (“lamproite”), showing dark volcanic clasts and a slightly lighter grey matrix of sand (with a spec of ‘fool’s gold’ in the middle). Photo taken by Andreas Zametzer, Research Associate at Curtin University. Image: AuScope edited

What instruments made this research possible, and what makes them impressive?

The biggest difference between the 1980s and now is the development of new analytical tools.

Principally, two techniques were used in this study. The first was automated mineral analysis, using a Tescan Integrated Mineral Analyzer housed in the John de Laeter. The “TIMA” maps out the minerals in a polished sample to quantify and aid in mineral relationship identification.

We could identify several minerals that we could date that were part of the volcanic eruption itself at Argyle, as well as the unconsolidated sediment that the volcano erupted into.

Sure, you can date grains in a sample willy-nilly, but without this level of contextualisation, you have no idea what event you’re really measuring.

Having established the minerals and the relative order in which these formed, we could then pinpoint specific ones we could date. And that’s where machine number two came into play - lasers and mass spectrometers housed in the GeoHistory Facility and WA Thermochronology Hub, both in the John de Laeter Centre.

A special shout-out to Auscope and NCRIS for these two laboratories. AuScope funded the original instruments in these laboratories and continues to provide salary support for technical staff. Without this support, there would be no way this research would happen.

GeoHistory Facility, Curtin University. Analyses were collected using the RESOlution SE laser and Agilent 8900 mass spectrometer. Image: AuScope edited

Describe the moment when you and your team realised you had rewritten timelines.

I remember sitting at my desk in early September 2022, having just processed the last of the data from Argyle.

Now, we didn’t have the perfect age, and, if I’m honest, with the alteration of the samples, I don’t think anyone will ever get the perfect age. But, we’d bracketed the Argyle volcanic eruption to between 1310 and 1260 million years ago, some 100 or so million years older than before.

My co-authors and I had a betting pool going as to what the age of Argyle really was. And we were all wrong.

But the significance didn’t dawn on me until I was cycling home that day. With blood pumping through my legs, I had the sudden realisation that it was about 1300 million years ago that the first supercontinent, Nuna, was breaking up.

The next day, I confided my hypothesis to Denis and Luc. Luc immediately began to look through reconstructions of tectonic plates using a program called GPlates, developed by the EarthByte Group in Sydney. Later that day, he showed me a reconstruction that confirmed my suspicions.

A supercontinent was breaking up. That was the trigger that shot Argyle to the surface. That was the missing ingredient to how pink diamonds form.

We needed not just continents colliding to turn colourless diamonds pink, but continents breaking up to bring these gems to the surface. And we needed to be at the edge of ancient continental blocks, like where Argyle was.

I was frantic. In less than two days, I’d written a draft of a paper, and after a few weeks of polishing with the help of co-authors, we’d submitted the article to the international journal Nature Communications.

What impact do you see coming from this research?

The ability to pinpoint where we can find more pink diamonds.

Shortly after the paper was published (mid-October), a private company contacted me saying they’d found half-a-percent of pink diamonds at their project at the edge of the Yilgarn Craton, exactly where our study of Argyle predicted they would be. For now, this region is subeconomic; there just aren’t enough diamonds to be financially successful.

Yet, it provides the first bit of evidence that other regions may be uncovered, giving us a new source of rare gems.

In contemplating such vast timescales, what reflections do you have on this moment in Earth’s history?

Whenever I think about our planet, I’m amazed that we’re the only one that sustains life. We are just in perfect balance in our solar system. And it’s wonderful to progressively uncover how Earth came to look like it does today.

Some 1300 million years ago, we were oh-so-very different from today. Almost all the landmasses were squashed together, almost ready to tear themselves asunder. It’d be amazing to stand at the precipice of a supercontinent breaking up into individual pieces and scary - imagine all the earthquakes and volcanoes!

I’m told that we’ll form another supercontinent in another 100 or 200 million years into the future. I surmise we won’t be around to see it, but it’s a fascinating thought nonetheless.

 
 
 
ECE, GPlates, SAMAuScope