19 Jun 2019

Questions have been circulating thick and fast about the huge diamond discoveries at LUCARA Botswana’s wholly owned Karowe Mine in Letlhakane, following the unearthing of huge and precious diamonds in the history of diamond mining in the country and the world over.

LUCARA made headlines through the discovery of a 1 109 carats diamond that came to be affectionately named Lesedi la Rona.

Lately Karowe Mine birthed yet another huge diamond (1 758 carats), which is yet to be named by Batswana.

It was against the backdrop of discovering diamonds exceeding 1 000 carats, setting tongues wagging in the diamond industry and populace platforms that the reporter undertook a mining expedition to unearth the secret by engaging LUCARA Botswana’s general manager, Mr Johane Mchive.

Mr Mchive pointed to the discovery of large diamond to employing the use of autogenous (AG) milling which eliminates chances of diamond damage found in traditional treatment plants. 

He said Karowe Mine was the second mine in southern Africa to commission the use of the AG mill in 2012 after Catoa Mine in Angola.

“The selection of the AG milling technology was based primarily on the fact that it was identified as the most appropriate and effective technology to reduce diamond breakage and improve recoveries across the full spectrum of diamonds, including the larger/exceptional diamonds instead of using extensive staged conventional crushing,” said Mr Mchive.

The AG mill, Mr Mchive said, was a product of previous research in the mining industry that had shown that diamond damage would continue to occur in traditional treatment plants.

The LUCARA Botswana boss explained that basic principles of operation of the AG mill was based on a rotating and lifting action of a large diametre cylinder relative to its length and to utilise large lumps of ore as the grinding media.

In this way, possibilities of breaking big diamonds were greatly minimised, if not eliminated altogether.

Unlike in the past decades, Mr Mchive explained that ‘diamond winning plants were focusing more on maximum diamond liberation through the deployment of conventional crushing technology which was known to be inefficient for the recovery of large stones in their natural and undisturbed state, hence the utilisation of the AG mill at Karowe Mine.

The LUCARA GM said the conventional crushing system had the potential to break diamonds and reduce chances of discovering magnificently huge stones as the technology used compression and impact forces between the steel surfaces to reduce the host rock into smaller sizes.

All the above challenges, as outlined by Mr Mchive, had the harmful potential of breaking large diamonds into smaller particles and hence long standing delays in discovering huge stones.

He said it was so because the AG mill contained compressive, shear and abrasive forces in a single device instead of using compression and impact forces between the steel surfaces to reduce the rock into smaller sizes in a multi crushing stages set-up which had the potential for breaking diamonds, Mr Mchive said in his response.

The process, according to the GM, minimised damage to diamond and maximised value in terms of revenue generated.

“The over-riding benefit of this technology is that it can be ‘tuned’ very easily for the purposes of operating at the correct level of liberation, striking a balance between value realised and operating costs,” he said, adding that AG milling, in conjunction with a diligent strategy of control became a business tool that delivered productivity over just production.

On other issues, Mr Mchive invited other diamond miners and producers to use Clara Diamond Solutions to sell their diamonds because of the principle of economies of scale.

The more diamonds there were in the platform, the better for diamond producers and manufacturers or retailers, Mr Mchive explained.

Amongst a myriad of benefits to the producers, the LUCARA boss enticed potential users that maximum selling price would be achieved for every stone, not reliant on tender cycles as well as eliminating sorting inefficiencies as a result of human inter alia. LUCARA has so far successfully made five sales through the Clara Diamond Solutions platform.

Quizzed about the security of the Clara Diamond Solutions, the LUCARA GM said it was very secure and added that like any other process, it would continually undergo improvements in all its totality.

This will be part of the continued refinery to gradually expand participation in the platform. ENDs