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Operated by De Beers between 1977 and

1982, Letšeng restarted operations in

2004 and was acquired by Gem

Diamonds (70%) in late 2006 for $118.5 million.

Its partner is the Kingdom of Lesotho (30%). It is

located in Lesotho’s Maluti Mountains at an

average altitude of 3,100 m above sea level and is

one of the coldest places in Africa. Visitors can

experience all four seasons at any time of year.

Letšeng is characterised by extremely low grade

ore (less than 2 ct/100 t), but is world famous for

giving up large diamonds, having the highestpercentage of large diamonds (greater than 10.8

ct) of any kimberlite, giving it the highest dollar

value per carat of any kimberlite diamond mine.

Historic diamonds are its forte, the most recently

recovered being 478 ct Leseli la Letšeng white

diamond – the world’s 20th largest rough gem

diamond and third significant recovery from the

mine in as many years, following the 603 ct

Lesotho Promise (14th largest) and the 493 ct

Letšeng Legacy (18th largest) recovered in 2006

and 2007 respectively. Including the 601 ct

Lesotho Brown, recovered way back in 1960 (15th

largest), Letšeng has now yielded four of the

world’s 20 largest rough gem diamonds and the

three largest gem diamonds recovered this century.

Letšeng processes ore from two kimberlite pipes

as well as from existing stockpiles. It has the

capacity to treat some 7 Mt/y of ore, producing

some 100,000 ct.

Man has always been prepared to go to the

end of the earth for diamonds and visitors to

Letšeng have to travel steep winding roads at

altitudes above 3,200m before reaching their

destination. On arrival, the view is majestic, with

sweeping vistas of snow capped peaks in all

directions bearing testimony to this remarkable

geological find, first discovered in 1957.

This is a tough operation, with the loading and

haulage component carried out by a 100% Caterpillar

equipment fleet run by specialist contractor,

Matekane Mining Investment Co (MMIC).As John Houghton, Letšeng’s Assistant General

Manager Production explains, that like most mines

it is an all day/all year operation, despite the

constant threat of inclement weather. “Snow,

which can fall at any time of the year, can close in

suddenly, bringing temperatures down to as low

as minus-15°C, but that doesn’t slow down the

mining operation, which remains at full tilt.”

Lesotho entrepreneur and Managing Director of

MMIC, Sam Matekane, secured the contract for

Letšeng in October 2007, and MMIC currently has

about 200 personnel on site, supported by a

technical maintenance team of 26 from

Barloworld Equipment (the Caterpillar dealer in

southern African). The mine’s technical capabilities

have been further enhanced following a R8 million

investment in new workshop facilities.

Letšeng did not slow production due to the

global economic crisis. And now that global

diamond sales are picking up again it maintains its

monthly output of around 450,000 t of kimberlite

and 660,000 t of country rock (basalt) from two

Gems from over

3 000 m

Letšeng, the world’s highest diamondmine, is internationally famed for itsgemstones of magnificent quality.John Chadwick first visited the mine atthe end of the 1970s

56 International Mining DECEMBER 2009

Letšeng mine

● S o

 u  t  h 

 A  f r  i c

 a

 S o u  t  h 

 A  f r  i c

 a

The Leseli la Letšeng [478] carat white diamond 

Butha-Butha

Hlotse

Teyateyaneng

Maseru

Mafeteng

Monhale’s Hoek

LESOTHO

Quthing

Qache’s Nek

Thaba-Tseka

Mokhotlong

GREAT MINES – Letšeng, Lesotho

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sources: the main pipe and the satellite pipe, both

of which have currently reached a depth of

approximately 120 m.

In the first half of 2009 Letšeng recovered 20

diamonds which sold at prices greater than

$20,000/ct, achieving an average price of

$29,563/ct. At the lowest point for rough

diamond prices in the first quarter of 2009,

Letšeng continued to operate at full capacity and

to perform optimally. In May 2009 the No 1 and 2

plants set a combined tonnage record.

Final depths for the satellite and main pipe are

estimated at 450 m and 550 m, respectively, with

an estimated life of mine at current production

volumes of more than 30 years. “The stripping

ratio on the satellite pipe is around 4:3:1 (or 4.3 t

of basalt for every tonne of ore),” explains

Houghton, illustrating the importance of the

effective planning and utilisation of theearthmoving fleet. “When you consider that

Letšeng typically yields below 2 ct/100 t it’s clear

that we expect maximum efficiency from MMIC

and our process plant contractors to keep working

costs at a minimum.”

The haulage unit is the Caterpillar 740

articulated dump trucks (ADT), 18 of these units in

total, 17 of which are constantly in production,

with one in reserve - with the oldest Cat 740 in

operation having already recorded 30,000 hours

(or around five years in service). Added to these

units are two Cat 385C and two 365 hydraulic

excavators; support equipment in the form of two

D6 and D8 dozers, a Cat 824 wheel dozer; two

140H motor graders; two 980 wheel loaders; two

wheeled excavators (a 316 and a 318 unit) fitted

with hydraulic hammers for secondary breaking of

large rocks; plus a 730 converted to a water cart.

The dozers are used on the waste dumps; to

control the pit floors; and for tailings processing,

with the bulk of their efforts focused on

rehabilitation, namely, topsoil stripping and

stacking.

MMIC’s Contracts Director, Ferreira Coetzee,

notes Matekane’s decision to opt for a 100%

Caterpillar fleet to maximise service and after-sales

support.

“Given the challenging underfoot conditions,

the Cat ADTs are far better suited than rigid off-

highway trucks in this terrain due to their all-wheel

drive capability, especially during the heavy snowfalls

traditionally experienced in the autumn and winter

months,” explains Coetzee. “As production ramps

up going forward, we anticipate that MMIC will

need to expand its 740 fleet to around 30 units to

keep pace with Letšeng’s demand.”

MMIC works on a three shift system, with the

average truck haul distance estimated at around

2.3 km. Productivity improvement assessments are

ongoing and include maintenance of the haul

roads and underfoot conditions at the loading and

tipping sites.

The Cat 385 and 365 hydraulic excavators are

the loading workhorses. “The Cat 365 units are

used to load the kimberlite (typically a blend of ore

from the main and satellite pit) – utilising some

45% of the ADT fleet – with the Cat 385s loading

the basalt,” says Coetzee. The size of the blasted

rock is around -750 mm for the basalt, and -450 mm

for the kimberlite, “with fragmentation at between

5 and 10% for oversize, which is where we use

our Cat wheeled excavators for final size reduction.

Obviously, the objective is to minimise the amount

of rehandling needed to optimise efficiencies.”

Coetzee says the mine is also considering the

use of a ‘rip and load’ method following an in-

depth feasibility study conducted by Barloworld

Equipment in conjunction with Caterpillar’s Work

Tools Centre in The Netherlands. Kimberlite has a

relatively low unconsolidated compressive strength

(UCS), so rip and load (using a specialised bucket

incorporating an excavation ripper) could, in

certain applications, contribute to a reduction in

the need to blast in specified mining areas.  IM 

Two Cat wheeled excavators (a 316 and a 318 unit)

fitted with hydraulic hammers undertake secondary 

breaking of large rocks

The Cat 365 units load the kimberlite (typically a

blend of ore from the main and satellite pit) - utilising

 some 45% of the ADT fleet - with the Cat 385s

loading the basalt 

GREAT MINES – Letšeng, Lesotho

DECEMBER 2009 International Mining 57