Southern Africa-focused precious gem producer Lucara Diamonds is finalising the optimisation of the newly integrated circuit as part of its flagship Botswana-based Karowe diamond mine’s plant optimisation project.

Lucara president and CEO William Lamb tells Mining Weekly that Karowe’s optimised circuit, valued at about $55-million, has been run at design capacity using different types of ore from the pit.

“Testing of the systems while processing the most difficult types of ore is in progress, with adjustments being made to the plant to accommodate these difficult ore characteristics.”

Lamb explains that the particularities of the feed material include high levels of high-density material, which causes complications in the dense-medium separation (DMS) plant and subsequent downstream recovery processes.

He, therefore, highlights that implementing the X-ray transmission (XRT) technology machines, as part of the plant optimisation, has significantly improved the early recovery of large high-value diamonds.

All material between 8 mm and 60 mm is subjected to the XRT technology, which looks for carbon, the main component of a diamond, as opposed to previous technology, which looked for the impurities within the diamond. This improves the upfront recovery of large diamonds and limits diamond damage, Mining Weekly reported last month.

“Since the machines were included as part of the full circuit, no less than five diamonds larger than 100 ct have been recovered by these machines, including three diamonds larger than 200 ct,” Lamb says.

He further stresses that to replace a coarse DMS circuit or have a smaller DMS plant and not require any further recovery processing requirements through the introduction of the XRT technology is “a significant game changer”.

This, linked with significantly higher throughputs, leads to smaller plants, lower capital outlay and diamond recovery closer to the front end of the plant before they could potentially be damaged, emphasises Lamb.

In addition to the XRT machines, Lucara has included two stages of magnetic separation in the recovery plant to remove magnetic material before it reaches the X-ray machines. While Lamb acknowledges that this technology is not new, he highlights the significant mass reduction effect that the stages have on the feed to downstream recovery processes.

“The upgrade is being completed to maintain the current throughput and production profile,” Lamb reiterates, reaffirming that sales from Karowe are still forecast at between 400 000 ct and 420 000 ct this year, at an operating cost of $33/t to $36/t of diamonds processed.

Exploration Sights
Lucara is also focusing on its two exploration licences in the Orapa/Letlhakana kimberlite district, in Botswana, with initial exploration still scheduled for this year.

Lamb notes that a bulk sample plant, located within the current Karowe mine lease area, is scheduled for final commissioning by the end of August.

Construction started on the bulk sample plant in April, with most of the early construction being civil works. Lamb explains that, as the plant is modular, all modules, including the front end, the DMS, degritting and recovery, were preassembled off site to ensure that everything fits.

“All modules, including the recovery, are now on site and construction is going well,” he says, pointing out that, as the plant is located within the Karowe mine lease area, access to water and power is ensured, and the need for generators eliminated.

When the processing of exploration samples is complete, the plant can also be used to do grade reconciliation and additional work on the Karowe asset, if required, Lamb adds.

“Lucara is awaiting permits from government to enable us to extract the 5 000 t samples from the kimberlite blocks BK2, AK11 and AK12,” he further notes.

Meanwhile, based on historical work, the three targeted kimberlites – BK2, AK11 and AK12 – were identified as being diamondiferous, Lamb says, but notes that Lucara aims to understand the value of the diamonds before spending the significant amount of money on the development of a grade model using large-diameter drilling.

Therefore, Lucara plans to extract and process 5 000 t of kimberlite from each of the three orebodies. “This will give us an indication of grade, but more importantly . . . the quality of the diamonds – a step that would historically only have happened at the end of the exploration timeline,” he says.

Lamb believes that exploration could result in two possibilities – “the first prize of a standalone orebody that can support a separate process facility, [or] the second prize of a resource with economics that will support the mining, transport and processing of diamonds through Lucara’s existing facility”.

“There definitely still is potential for economic kimberlite discoveries in Southern Africa. The resources may not be as large but the model we have implemented proves the economic extraction of value from smaller assets,” Lamb concludes.