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Labs Identify Fingerprint for Argyle Pinks

Diamonds from Rio Tinto’s Australian mine exhibit blue fluorescence under ultraviolet light.
Nov 4, 2019 6:07 AM   By Leah Meirovich
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RAPAPORT... Two gem labs have joined forces to identify a method for determining whether a pink diamond came from the Argyle mine in Australia, and are issuing lab reports confirming their provenance.

Beginning in 2014, the team, led by Branko Deljanin, director and colored-diamond specialist at Canadian Gemlab (CGL), began collecting natural pink diamonds from the mine in Western Australia, as well as from six other countries. It also tested pink synthetic diamonds grown using chemical vapor deposition (CVD) and High Pressure-High Temperature (HPHT), as well as those that were irradiated or annealed.

CGL and GemResearch Swisslab (GRS) found that Argyle stones typically gave off blue light when under an ultraviolet lamp, with the nature of that fluorescence changing depending on whether they are exposed to short-wave or low-wave rays. Stones from Canada, Siberia, Brazil and Africa did not fluoresce at all.

This discovery led them to define Argyle pinks as type IaAB, which separated them from pink diamonds found in other countries. The group also uses spectroscopy tests, such as infrared and photoluminescence, to confirm the provenance, Deljanin told Rapaport News.

While Argyle has produced pink diamonds since 1985, owner Rio Tinto only began laser-inscribing the stones in 2005, according to Deljanin. The miner also only tags stones above 0.20 carats, while CGL and GRS can test pink diamonds as small as 0.02 carats. The ability to differentiate Argyle diamonds has become more important as the mine reaches its end of life in 2020.

“There is a 15% to 30% premium on pink diamonds with proven Argyle origin,” Deljanin explained, noting that both CGL and GRS could test unmounted stones and issue a report stating a diamond originated from Argyle.

The labs can also differentiate between greyish-blue Argyle diamonds and those from other parts of the world, Deljanin added. Those originating in Western Australia contain impurities such as nitrogen and hydrogen, while those found in other areas, such as Brazil, South Africa or India, are colored by boron.

Deljanin’s initial phase of research was sponsored by Rio Tinto, while the latter part was sponsored by GRS Hong Kong.

Correction, November 5, 2019: This story has been updated to reflect the fact that Rio Tinto only sponsored the initial phase of the research.

Image: Pink diamonds from the Argyle mine. (Rio Tinto)
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Tags: Argyle mine, Argyle Pinks, Branko Deljanin, Canadian Gemlab, CGL, GemResearch Swisslab, GRS, Leah Meirovich, Rapaport News, Rio Tinto
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