Modern Mining

March 2016



MODERN MINING



feature

DIAMONDS

he deposit at Lerala comprises a

cluster of five diamond-bearing

kimberlites – designated K2 to

K6 – which were originally dis-

covered by De Beers in the early

1990s. KDL will be the fourth company to mine

at the site. De Beers undertook a trial mining

programme starting in 1997 but decided that

the Tswapong project – as it was then known –

did not meet its economic criteria. ASX-listed

DiamonEx later picked up the project and built

the present mine infrastructure but had the

misfortune to bring the mine on line when the

global resources market was in disarray follow-

ing the global financial crash of 2008.

A third company, Mantle Diamonds, oper-

ated the mine for a few months in 2012

producing approximately 73 000 carats. A

range of technical issues in the processing

plant, however, resulted in poor recovery and

led to the mine once again being put on care

and maintenance.

KDL acquired the project in early 2014 and

is confident that it can succeed where its prede-

cessors have failed. It announced in September

2014 that South African engineering company

Consulmet had been appointed to design mod-

ifications to the plant intended to facilitate

dramatically improved diamond recovery and

throughput reliability. Consulmet was subse-

quently engaged to execute the plant upgrade

and refurbishment on an LSTK basis.

The upgrade and reopening of Lerala is

costing A$14 million (with the plant modifica-

tions accounting for A$9,4 million). The mine

– which has a 20,1 Mt resource with an average

grade of 24,2 cpht – will have a life of nine years

and is expected to generate a net cash flow of

A$165 million over this period. Average annual

production is estimated at 336 000 carats.

Approximately 1,4 Mt of ore will be

produced annually

with the mining

being handled by

a mining contrac-

t o r, Ba s i l Re a d

Botswana. The con-

tract covers the initial five years of mining and

its value is around A$47 million at current

exchange rates. Basil Read Botswana was due

to start mining this month (March), starting in

the dewatered K3 pit.

The upgraded plant is a conventional dia-

mond processing facility incorporating primary,

secondary and tertiary crushing and associated

screening; primary and secondary scrubbing and

screening; and gravity concentration via a DMS

module with dual cyclones which are fed fines

(+1 mm/-6 mm) and coarse (+ 6 mm/-18 mm)

product streams. Sink screen concentrate is

pumped to a new recovery module which will

classify and dry the concentrate prior to X-ray

sorting and final recovery by hand sorting, all

within a new secure recovery facility.

The completely new recovery section is

designed to enhance first pass diamond recov-

ery and minimise diamond loss while the new

secondary crusher is expected to improve dia-

mond liberation and processing reliability. A

scrubber and trommel have been added to the

plant to handle wet ore and maintain through-

put while additional surge capacity will

decouple sections of the plant, reduce down-

time and maintain head feed rates. Automated

thickener control will ensure a consistent and

optimised tailings treatment philosophy.

The mine and processing plant are powered

by diesel gensets and source excess water via a

pipeline from the Seleka wellfield. Labour and

services will be sourced from the local villages

including the Lerala village, located 10 km

south-west of the 21,86 km

mining licence.



Lerala

on the brink of production

The new platform for the

primary scrubber (left fore-

ground) ready to accept the

scrubber shell, the primary

crusher (rear) and the re-

furbished conveyor (photo:

Kimberley Diamonds)

Botswana’s Lerala diamond mine near the border post

of Martin’s Drift – which was originally commissioned in

2008 but placed on care and maintenance early in 2009

– is on the brink of recommissioning, with first diamond

production expected in April. The owner, ASX-listed,

Kimberley Diamonds Limited (KDL), has all but completed

an extensive refurbishment and upgrade of the process

plant designed to allow it to achieve a reliable throughput

of 200 t/h and enhanced diamond recovery.

KDL acquired

the project in

early 2014 and

is confident

that it can

succeed where

its predecessors

have failed.