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X-Ray Transmission technology: a true game-changer for diamond mining

TOMRA Mining COM XRT installation at Letseng mine

The big challenge in diamond mining is not only to find the diamonds hiding in the rock, but very importantly to extract them minimising breakages and dealing with waste effectively and cost efficiently. In recent years, X-Ray Transmission (XRT) technology has attracted increasing interest in the industry for the exceptional capability it has shown in addressing these issues with unparalleled success. The Letšeng mine in Lesotho is an excellent example of how XRT sensor-based sorting technology can unlock significant value and deliver an exceptional return on investment.

29 November 2021

Gem Diamonds, a leading global diamond producer of large high value diamonds, owns 70% of the mine, which is located in Lesotho’s Maluti Mountains. One of the largest open pit diamond mines in the world, it processes ore from two kimberlite pipes – the Main pipe (17.0ha) and Lesotho Legend diamondthe Satellite pipe (5.2ha) – and is known for the recovery of Type II diamonds. The ore is treated through two plants with conventional crushing, scrubbing, screening and Dense Medium Separation (DMS) processes. The DMS concentrate is split into three fractions that are sent to be processed with XRT (X-Ray Transmission) and XRF (X-Ray Fluorescence) technologies. In 2017, the company undertook several activities to unlock the mine’s full potential and contacted TOMRA Mining to explore ways of improving its Coarse Recovery process. Extracting value from historic tailings: increased recovery and revenue Jaco Houman, Senior Manager Technical and Projects at Gem Diamond Technical Services, explains: “We had quite a lot of historic tailings material. We had a view that we weren’t quite getting all the diamonds we were looking for.”

Gem Diamonds rented a TOMRA COM Tertiary XRT sorter to evaluate the sorter as a recovery and bulk sorting unit. The initiative was a success and the sorter exceeded all expectations: “The unit showed that it recovers consistently from the tailings material. The value that came from it spoke volumes about the technology and the potential that could still be obtained with the material available. It cemented the realisation that we needed a recovery unit for scavenging, auditing and second-pass recovery.”

TOMRA COM XRT 2.0 sorter recovers 15 times initial investment in 4 years

TOMRA Mining installation at Letseng mineAt the end of the rental contract, Gem Diamonds purchased a TOMRA COM XRT 2.0 sorter to replace the rented sorter. Featuring a bigger ejection chamber, higher belt speed and throughput, this unit was perfectly suited to the large diamond recovery set up the company was looking for.

The results arrived immediately: “In January 2018, we had pretty much just finished commissioning this unit and we recovered the biggest stone Letseng had ever seen, the 910-carat Lesotho Legend. There was no question about performance after that,” says Jaco Houman. “Since 2017, we have recovered 6 diamonds that were sold for more than 1 million US$ with the two TOMRA XRT sorters.”

With the TOMRA COM XRT 2.0, by 2021 the mine’s +5mm historic material had been depleted. The focus shifted to scavenging and auditing the existent tailings, as Jaco Houman explains: “By having this unit in place, we are now able to recover all the diamonds that are present in our concentrate, either through a first or a second pass.”

With its performance, the TOMRA COM XRT 2.0 sorter has more than paid for itself, having recovered about 15 times the investment value over the 4 years it has been in operation.

Breaking new ground with the first TOMRA XRT Final Recovery sorter in the world

TOMRA employees at Letseng mineHaving found an effective solution for Coarse Recovery, Gem Diamonds turned their attention to the Fines Recovery Circuit and opted for TOMRA’s ground-breaking Final Recovery sorter. “We wanted to find a solution to increase our revenue from the treatment of historic material,” says Jaco Houman. “We were looking for a compact machine we could use as a final recovery sorter, and the TOMRA COM XRT 300 /FR performs very well in that duty, or even as a single particle sorter. Also, it is a sorter that will treat a super-concentrate and work very well as a scavenging unit.”

“The diamond industry had been waiting for 20 years for a way to introduce XRT directly into the Diamond Final Recovery instead of the bulk concentration stages where the DMS modules exist,” explains Ryan Szabo, Sales and Project Manager Diamonds at TOMRA Mining. “The TOMRA COM XRT 300 /FR is the first to accurately sort diamonds based on their properties and not their proxies, achieving market leading recovery with the highest recovery factor to date.”

TOMRA’s Final Recovery sorter performed well right from the commissioning stage. In the words of Ryan Szabo, “it was the most successful first implementation of a new solution that TOMRA has ever had.”

TOMRA: invested in the client’s success

The last four years have seen the successful introduction of TOMRA’s XRT technology at the Letšeng Diamond Mine, where it has provided effective solutions in different stages of the process, improving the operation’s profitability and efficiency. For Jaco Houman, this success stems not only from the advanced technology, but also from TOMRA’s approach to serving its customers: “What I like about TOMRA, is that for them it’s not just about selling you a piece of equipment. If the equipment doesn’t work in the solution or the system that you want, they’d walk away from the sale. For me, this testifies to the fact that they have a vested interest in the success of your business. We’re dealing with an organisation with experienced, professional people. I believe that when TOMRA makes a commitment, you can bank on the fact that they will deliver on that.”

Overview of Letseng mine