One Mine, 4 Geologist, 37 Years of Global Impact

On November 3, 2020 the Argyle Mine of Australia officially stopped production. Despite multiple continent, scientific, and cultural impact spanning 37 years, most people reading this will never have heard of it, but its existence changed the world in many different ways. This is a story of strange geology, incredible perseverance, a desire to remove old shackles, the quest for opportunity, and cultural changes that permeated global markets. You have seen these changes all around you but didn't realize their source or history. Continue reading to understand how a single mine in Western Australia changed the world around you!

The Way it Started: Most people in undergraduate level geology courses are taught that diamonds are found in kimberlite pipes. These igneous rocks bring diamonds to the surface from depths of 100-280 miles (150-420 km) below the surface, originating deep within the Earth's mantle. The volcanic eruption that emplaces a kimberlite pipe is rapid and violent. The last known kimberlite eruptions were ~10,000 years ago in Tanzania, but these were not diamond bearing. There have been four significant periods of kimberlite activity: 1.2-1.08 Billion years ago (Mesoproterozoic), 600-500 Million years ago (Neoproterozoic), 400-350 Million years ago (Devonian), and 250-50 Million years ago (Triassic - Eocene). As the kimberlite magma reaches the near surface, an eruptive blowout occurs, which ultimately results in a crater. The crater is often filled with breccia and surrounded by a tuff ring. If, through time, the crater and the tuff ring are preserved, one can find diamonds in these features. But often the explosive material, and even the top of the pipe, can be eroded and reworked resulting in a nearby alluvial facies from which recycled diamonds can be extracted. In fact, prior to the discovery of kimberlites, diamonds were mined from these secondary alluvial deposits. Due to the extensive history of diamond exploration in South Africa, much of what we learn in school is derived from there. In fact, the term "kimberlite" is from Kimberly, South Africa, where the first diamonds were discovered in the country and kimberlites were first found. Worldwide, about 6400 kimberlite pipes have been discovered, only ~1000 are diamondiferous. Of those, only 50 were economic. So, many of us live our geologic lives thinking that although not all kimberlites contain diamonds, all diamonds come from kimberlites.

Enter Western Australia: For many years, starting in the 1890's it was known that diamonds could be found in the alluvial sediments in Western Australia, usually stumbled upon by accident those prospecting for gold in streams. However, large diamond deposits were not found. In 1960, RT Prider hypothesized that diamonds in western Australia could be coming from lamproite rather than kimberlite, an unusual and interesting idea, but still did not lead to a diamond deposit discovery.

In 1972, a young female geologist named Maureen Muggeridge, a recent graduate of St Andrews University in Scotland, emigrated to Perth, Australia. With no more than ￡10 in her pocket, and a dream driving her, she spent her first night sleeping under a palm tree in Perth's Kings Park. Weeks later, she landed a job as part of the initial thrust of major diamond exploration in Western Australia, which seemed like a joke, since Australia wasn't known for diamonds at the time. Within a year she had found a diamond-bearing sample at Pteropus Creek, the first discovery in Western Australia. She went on to discover other deposits, including during a diamond rush in 1978, where she beat a competitor by working by moonlight to place four claims.

Muggeridge was responsible for managing many diamond exploration programs in the 1970’s and 1980’s. She worked for the Ashton Joint Venture, as it eventually came to be known, managing a diamond exploration project in the ironically named Kimberly region of Western Australia. As such, she spent many months doing fieldwork and conducting helicopter-borne sampling surveys each year.

Generalized map showing the locations of kimberlites, lamproites, and diamond occur-rences in the Kimberley craton region of WesternAustralia, including the Argyle mine (east of theKimberley craton). From Shingley et al 2001.

De Beers had previously spent ￡10 million searching for diamonds in the Kimberly region, specifically the area around Smoke Creek where hints of diamonds kept coming up, but no clear discovery had ever been made. In fact, apart from an area of diamond pipes in the Ellendale district in the west Kimberley, which proved to be uneconomic, little was found. However, Muggeridge and her then husband, John Towie, persisted in evaluating the area around at Smoke Creek. In July, 1979, they discovered the first major diamondiferous deposit at Smoke Creek, and what was to become one of the world's most important diamond mines - Argyle. Muggeridge was 6 months pregnant at the time. In an attempt to thwart competitors, a campaign of misinformation was launched, suggesting that work in that area had been put on hold due to Muggeridge's pregnancy, when in fact, Muddgeridge and her team continued to trace the alluvial deposits to find the pipe source. On 2 October 1979, geologists Warren Atkinson and Frank Hughes found the volcanic pipe, after spotting a small diamond embedded in an anthill, in the ranges halfway between Lake Argyle and the Bungle Bungles.

The Argyle Mine and the surrounding rugged terrain. From Rio Tinto

The Argyle pipe was the first major diamondiferous ore deposit found hosted by lamproite, not kimberlite. It is located in a Proterozoic orogenic belt at the craton margin, a setting not previously considered prospective for diamond pipes. The Argyle lamproite is a 2-km-long, north-northeast trending, elongated, tilted vent, intruded 700 million years after the main orogenic activity in the Halls Creek Mobile Zone. This discovery changed geologic thought about diamond deposits, diamond evolution, and how diamonds move from the mantle to Earth's surface.

Changing Supply Chains & Perceptions: The discovery of Argyle didn't just change geologist's understanding of diamonds, it resulted in a reinvention of diamond marketing, the diamond supply chain, and people's perceptions. The Argyle pipe - AK1 - almost immediately became the world’s largest source of diamonds by volume produced. In a single volcanic pipe, the searchers had found as many diamonds as there were in all the world’s active diamond mines at the time, which didn't take into account the volume of alluvial diamonds. But, although highly productive, the diamonds were dominantly small and ranged from near colorless, to yellow, to brown in color. With 80% being brown diamonds, the company realized it faced a high level of resistance to this material at the retail level. There was also the issue of the high volume of small diamonds. All of the major diamond cutting centers (NYC, Tel Aviv, Antwerp) did not cut small diamonds because it is very labor intensive relative to the size of the gem. They were also not interested in brown diamonds as they perceived them to be of only industrial value.

Three cognac-colored diamonds from Rio Tinto's Argyle mine in Western Australia clearly demonstrate the beauty of brown diamonds after cutting and placing in jewelry design. Image 2016 Rio Tinto.

Rio Tinto, the mine's owner by now, decided to change the value of their material. By the late 1980s, Australia’s Argyle mine had become one of the world’s largest producers by volume of rough diamond. At first, they joined the established single-channel distribution system of the Central Selling Organization (CSO) - De Beer's trading arm - and sold 75% of its production to the CSO, which carefully controlled the release of rough diamonds to the global market. However, that relationship became strained due to the restrictions imposed by De Beers on Argyle's famous pink diamonds - its most valuable commodity. The Argyle mine is most well-known for consistently producing beautiful, rare, pink, red, and violet diamonds. By volume, these are a tiny fraction of the diamonds produced at Argyle but are some of the most valuable diamonds produced anywhere. This one mine produced 90% of the pink diamonds in the world. (Most articles about the Argyle mine discuss the pink diamonds because they are so valuable, not this story)

Range of color saturation in brown diamonds. Photo by Maha Tannous, from Shigley et al, 2001

Argyle owners began their reinvention by taking responsibility for producing, cutting, and marketing their own product, starting with small and brown diamonds. They turned to the nascent Indian cutting industry to fashion what was once consigned to industrial use into jewelry ready pieces. Argyle began working with diamond cutters in India rather than the major diamond cutting centers because labor costs were not only lower, but India was also anxious to expand their labor force skill-sets. As stated earlier, the smallish material requires intense effort, which the Indian groups brought to the table. They also brought innovation by introducing diamond-impregnated polishing discs into the cutting process. This tool prevented some of the more brittle stones from breaking, thereby preventing additional loss of material and improving efficiency. An entire generation of diamond cutters gained expertise working on Argyle diamonds. The cutters in India became more adept at diamond cutting, also expanding into larger stones, as well as dominating the smaller stone market, creating a new powerhouse diamond cutting center. By 2007, India was cutting 90% of the world rough diamond supply by volume, making it the dominant cutting center. But they didn’t stop there! In 2008, highly skilled Indian diamond cutters started training African diamond cutters and helping countries there set up their own processing centers for material mined there.

By 1996, the relationship between De Beers and Argyle had totally collapsed, which left Argyle in complete control of its own material. After setting up the processing relationship with India, Argyle then began marketing cut, non-colorless stones as "cognac" or "champagne" diamonds. They also began promoting more affordable jewelry pieces studded with tiny gems, which opened the market of diamond jewelry to a much wider audience. Jewelry with small, more affordable diamonds became more and more popular across the globe as people not only began admiring the new jewelry designs, they were also able to afford them! Argyle had turned a rejected product into a new and profitable niche in the diamond jewelry market.

Le Vian? graphic for jewelry using Chocolate Diamonds?, highlighting affordability in rare colored diamonds.

In 2000, family owned Le Vian? initiated a campaign to differentiate high saturation brown diamonds under the brand Chocolate Diamonds?. To be branded as Chocolate Diamonds?, these need to rate high saturation of color, have a clarity of SI1 or better, have a specific hue, be within the top 5% of the production, and sourced by Le Vian?. In the world diamond production, Chocolate Diamonds? of 20 points or larger are 10,000 times rarer than white diamonds, but also are the most affordable of the fancy-colored diamonds. Le Vian? decided to build a brand around them, and in doing so revolutionized fine jewelry by combining the multiple colors of diamonds, gems and gold in new ways. Virtually all of Le Vian? Chocolate Diamonds? are produced from the Argyle Diamond mine. Today, the brand continues to rise in popularity as one million strong Le Vian? followers - a collector base that includes royalty, celebrities, socialites and everyday people. Today, the term “chocolate diamonds” is used ubiquitously by the public, not just referring to the branded diamonds from Le Vian?. Searches for “chocolate diamonds” exceed 100,000 per day on Google and returns 180 million results.

Conclusion: November 3, 2020 marked the closing of the Argyle Mine. Multiple articles have been written about the loss of the pink, red, and violet diamond supply, and how the mine’s closing will impact prices for those. I wrote this article because focusing on the impact of just the pink diamonds misses the incalculable impact this mine, and its history, has had on the world around us. Argyle changed our understanding of geology and deep Earth processes. Its discovery by a woman & man team demonstrated the equality of both in this scientific field at a time when that was not commonly seen. Rio Tinto’s perseverance against established supply chains and industry perception changed the lives of Indians and Africans who are now be able to determine their own destiny in the jewelry trade – a ripple effect across multiple continents. Rio Tinto’s marketing genius brought diamonds to the masses by demonstrating the beauty of using combinations of small gems in jewelry styles. Rio Tinto created a market of colored diamonds that are affordable to those who are not royalty. Le Vian took those diamonds and created an American brand whose goal of colorful, beautiful, and unique has now permeated into mass culture. All of this, over 37 years, from one mine found by four geologists in rugged Western Australia.

References:

Karma Barndon, 2020, Rio Tinto's Argyle Shuttered, Mining Magazine, (https://www.miningmagazine.com/life-cycle-end-of-life-management/news/1398561/argyle-shuttered)

Jelsma H., Barnett W., Richards S., Lister G., 2009, Tectonic setting  of kimberlites. Lithos, vol.112, pp.155–165, https://dx.doi.org/ 10.1016/j.lithos.2009.06.030

Brown R.J.,etal., 2012, Eruption of kimberlite magmas: Physical volcanology, geomorphology and age of the youngest kimberlitic volcanoes known on Earth (the Upper Pleistocene/Holocene Igwisi Hills volcanoes, Tanzania), Bulletin of Volcanology, vol.74, no. 7, pp.1621–1643, https://dx.doi.org/10.1007/s00445-012-0619-8

Jaques, A.L., Luguet, A., Smith, C.B., Pearson, D.G., Yaxley, G.M., and Kobussen, A.F., 2018, Nature of the mantle beneath the Argyle AK1 lamproite pipe: Constraints from mantle xenoliths, diamonds, and lamproite geochemistry: Society of Economic Geologists, Special Publication 20, p. 119–143.

Stuart Kells, 2020, Op-ed: The Argyle mine is important globally, and locally, The Mandarin, (https://www.themandarin.com.au/144431-op-ed-the-argyle-mine-is-important-globally-and-locally/)

Hobart M. King,, Brown Diamonds (https://geology.com/gemstones/brown-diamonds/)

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Prider R.T. (1960) The leucite-lamproites of the Fitzroy Basin,Western Australia. Journal of the Geological Society of Australia, Vol. 6, Pt. 2, pp. 71–120.

Rayner M.J., etal., 2018, The geology of the Argyle (AK1) diamond deposit, Western Australia. Society of Economic Geologists Special Publication, no.20, pp.89–117.

James E. Shigley, John Chapman, and Robyn K. Ellison, 2001, DISCOVERY AND MINING OF THE ARGYLE DIAMOND DEPOSIT, AUSTRALIA, Gems & Gemology, Spring 2001 (https://www.gia.edu/doc/Discovery-and-Mining-of-the-Argyle-Diamond-Deposit-Australia.pdf)

Steven B. Shirey and James E. Shigley, 2013, Recent Advances in Understanding the Geology of Diamonds, Gems & Gemology, Winter 2013, Vol. 49, No. 4 (https://www.gia.edu/gems-gemology/WN13-advances-diamond-geology-shirey)

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