A huge trench cutter rig operated by Rio Tinto will excavate a massive hole starting in the spring as the mining company aims to determine the amount and value of diamonds buried in the kimberlites at Fort à la Corne east of Prince Albert.(submitted photo/Star Diamond Corp.) : Glenn Hicks

By Glenn Hicks

DIAMOND MINING

Study shows unusually high proportion of high-value diamonds: Star Diamond

Mar 6, 2019 | 5:37 PM

As mining giant Rio Tinto gears up for large bulk sampling of diamonds at the proposed Fort à la Corne mining site east of Prince Albert, the owners of the kimberlite deposits are releasing information they say gives them optimism for the discovery of very large stones in future.

Star Diamond Corporation said results back this week from the Saskatchewan Research Council show an unusually high proportion of so-called Type II_a diamonds from a sample of 7,000 stones taken from an evaluation parcel at the Star and Orion South deposits between 2004 and 2009. The stones were analyzed in detail and these results confirm an earlier study of 260 stones from 2010.

“We hope to see diamonds over 100 carats” – _{George Read, Star Diamond Corp}

“Type II_a stones are exceptionally rare and account for less than two per cent of diamonds mined from kimberlites worldwide,” George Read, the company’s vice president of exploration and development told paNOW. “We were able to show that in the case of the Star deposit over 26 per cent of the diamonds fall in the Type II_a category and it is 13 per cent in the Orion South deposit.”

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Read said these diamonds can be the most unique top colour ‘white’ and all of the top 20 large diamonds ever recovered worldwide have been Type II_a.

“The net result of this is that we would be optimistic to say that in future production we would hope to see [high-value] diamonds over 100 carats and we would like to think that a number of those would have these exceptional top colours,” he said.

At the extreme end of the price range these types of diamonds can fetch, Read said the 813 carat ‘Costellation’ stone was sold for a record price of US $63.1 million. That came from the Karowe mine in Botswana.

So far the most valuable Type II_a stones recovered from the evaluation parcel at the Fort à la Corne site was 11.9 carats from Star, and a 15.8 carat stone from Orion South. Read said these were valued at US $11,333 and $2,800 per carat respectively. That would value these two individual stones at around US $134,000 and $44,240.

Read said Rio Tinto would be using the latest high-tech drilling, cutting and processing procedures to minimize the potential breakage of large stones that may occur in their large bulk sampling.

Rio Tinto, which can earn up to a 60 per cent stake in the potential mine, has not given any indication as to whether a project would be financially feasible. Their bulk sampling and processing of the kimberlites will help determine that, but officials with the mining company have said it could take years for definitive answers.

Read said core and sonic drilling was currently underway to understand the geology of the bulk sampling site. Among other current developments was the delivery of 22 of 25 containers filled with the components of a pre-manufactured processing plant that was made in South Africa.

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glenn.hicks@jpbg.ca

On Twitter: @princealbertnow