Kimberley's diamond endowment given new sparkle

JOHANNESBURG (miningweekly.com) – Generations of diamond processing experience, interwoven with modern know-how, is extending the diamond endowment of the city of Kimberley.

Kimberley Ekapa Mining Joint Venture (KEM-JV) has come up with a viable business model that returns a diamond sparkle to the city renowned for its 19th-century diamond mines and hand-dug Big Hole.

The historical surface dumps that De Beers left across the Kimberley landscape – together with the Kimberley Underground Mines sold by De Beers to Petra Diamonds six years ago, as well as the remaining underground resources at Dutoitspan, Bultfontein and Wesselton – are now all available to KEM-JV, which has succeeded in erasing 2018 as the scheduled shutdown year for Kimberley’s diamond operations.

Provided the operations are not further negatively impacted by the current immense illegal mining activities experienced in the area*, KEM-JV intends keeping diamond operations going for at least another ten years with a 20-year target, which represents an extremely substantial contribution to the economy of a city that has depended on the diamond industry for more than 130 years.

“It’s exciting for us to be able to extend the diamond life of Kimberley. It’s a great achievement by the teams and the companies that have put it all together,” KEM-JV CEO Jahn Hohne told Mining Weekly Online in an exclusive interview.

Hohne has led the charge with the help of diamond expertise his family built up over generations.

He has confronted the reality of tailings’ values declining with recency, and is turning to positive account a mix of low-grade fine material from surface and virgin kimberlite material from underground.

These materials are being processed in a rejigged and upgraded former De Beers Combined Treatment Plant (CTP), now boosted by a fully automated, ultra-modern rotary pan plant.

The throughput is currently at 26 000 t/d with a target of 27 000 t/d, up from the previous 20 000 t/d, made up of a combination of tailings and fresh underground material.

“We now have twelve 16 ft pans running beautifully,” commented Hohne, who has in the past 30 years operated plants with pan sizes of 2x12 ft, 4x14 ft and more recently 7x15 ft – but never at his career best 12x16 ft.

Mining Weekly was present at the opening by De Beers in 2004 of the CTP, a dump recycling facility made up of primary diamond liberation processes, dense media separation (DMS) concentration and X-ray final recovery.

However, its capacity of 500 000 t/m, or six-million tonnes a year, coupled to newer dumps having lower grades, proved inadequate for the KEM-JV model.

This resulted in the KEM-JV’s decision to increase the plant’s capacity by 50% to nine-million tonnes a year for economy of scale benefits, with its equipping directed towards the optimal processing of fine dump material together with coarse primary-crushed underground ore.

A 1.5 km extension conveyor belt, built in four months, now delivers tailings at lower cost than trucks can do, from the outlying dumps to the CTP, which formerly housed two significantly under-utilised 400 t/h tertiary crushing high-pressure grinding rolls.

Playing a key role currently is the automated pan plant, with the name given to it – a play on the ‘Great Escape’ movie Papillon – providing a glimpse of the dogged determination, commitment and perseverance that has gone into extracting gain from Kimberley’s declining tailings’ values.

“I’m very pleased to say that we’ve hit the green button, popped the champagne and named the plant PiPillon,” Hohne told Mining Weekly Online, while revealing that the letters of the acronym stand for “proportional intelligent pans with integrated liberation and logic online”.

“It’s quite special,” he commented, in describing his career high point.

To accommodate the throughput of lump-size primary-crushed underground material, an additional 250 t/h deep-cone secondary crusher has been installed and pre-concentration introduced to overcome the inadequacy of the fines DMS circuits.

Only two of the six DMS circuits, each operating at a rate of 110 t/h, are now directed at - 6 mm fines concentration, and three, each operating at a rate of 220 t/h, undertake coarse concentration, with one DMS circuit spare for redundancy.

The dozen 16 ft (4.9 m) pans, each with capacities of 50 t/h to 60 t/h, have been positioned close to the CTP’s scrubber section to receive the - 6 mm complement of the scrubbed material.

Up to 700 t/h of the head feed of 1 400 t/h is pre-concentrated to 20%, with the lightweight 80% portion discarded to tailings.

The upshot is a capacity increase to 1 400 t/h from 950 t/h, or to 750 000 t/m from 500 000 t/m, or to nine-million tonnes a year from six-million tonnes a year.

The pan plant and entire CTP circuits make use of supervisory control and data acquisition including programmable logic operational controls, balanced with algorithmic intelligence automation.

OPERATIONAL SHUTDOWN AVERTED

While the shutdown of Kimberley’s diamond operations has been averted, Hohne is urging the city to plan for a soft landing beyond 2030, as no additional major diamond discoveries are expected in the immediate well-explored Kimberley area.

There is a chance that the success of KEM-JV in processing lower grades with Proportional Intelligent Pans may attract the attention of many diamond processing operations globally as well as the Jagersfontein retreatment operation, which is 160 km away, in the Free State. This operation is using DMS circuits to recover diamonds from the tailings dumps that De Beers sold to independent diamond miner Chris Potgieter and billionaire Johann Rupert several years ago.

Unlike the situation in Kimberley, where 27 000 t/d throughput is made up of surface tailings, including approximately 6 000 t/d to 7 000 t/d of underground material, at diamond mines like Cullinan, Finsch and Koffiefontein the reverse pertains, with underground mining being the primary activity and tailings retreatment playing a secondary supplementary role.

The big Botswana mines are all modern mines that use low-value tailings to supplement underground material, leaving Kimberley in the sweetest spot when it comes to extracting value from historic diamondiferous mining waste, built up at a time when relatively rich discard was dumped owing to the technological constraints of the time.

KEM-JV deserves great credit for managing to keep Kimberley’s diamond sparkle alive and ensure that the important benefits it generates continue to flow into the capital city of the Northern Cape and its economically constrained surrounds.

* A follow-up article will cover the severity of illegal mining on the industry.