CEN JUL
18
IN EARLY 2010
, three independent experts undertook a resource statement for Ghaghoo,
which determined Ghaghoo’s total carat resource to be 20.5-million carats with a total
in situ
value of US$3.3-billion.
Two blue diamonds were recovered from samples during the valuation work – a find of some
significance in such a small parcel, given the extreme rarity of these diamonds. As a result of
the findings, in August 2010, Gem Diamonds presented the Botswana Government with an
updated study on Ghaghoo, including the option of an underground mine. Upon acceptance,
Gem Diamonds’ board approved a capital budget of US$87-million for the construction of
Phase 1 of the Ghaghoo Diamond Mine project – a mammoth task, which Redpath Mining
South Africa was well placed to take on.
Redpath Mining South Africa’s General Manager of Mining, Jan van Antwerp, says that the
company’s overall scope of involvement in the project involved the development of a concrete-
lined decline tunnel to 112 metres below the surface, at an inclination of eight degrees, using
an open faced tunnel shield (OFTS), which weighs 50 tons and has a diameter of six metres.
Jan explains that the project began with the establishment of a box cut measuring 25 metres
deep and 171 metres long. “Once the box cut had been developed and the portal support
was in place, Redpath began excavation work for the sand tunnel, measuring 403 metres in
pure sand and 121 metres in basalt. The tunnel is made up of concrete rings consisting of
ten 75mm thick segments. The rings are designed to withstand a compressive force of 45mPa
but are only required to withstand about 30mPa. The tunnel has a diameter of 6.1 metres.”
When completed, the tunnel will be made up of 8450 segments, consisting of 845 rings.
“The width of each segment for this particular project is 0.61m, and we are aiming to move
forward six segments or 3.6m-per-day,” he explains. This is accomplished by digging up to
0.7m and loading the sand onto the conveyer belt before it is fed out of the mine, and pushing
the OFTS into that space.
Ground-breaking
sand tunnel
Contract firm Redpath
Mining South Africa’s
involvement in the
sinking of a one-of-
a-kind decline sand
tunnel for junior
miner, Gem Diamonds’
Ghaghoo Diamond
Mine project in
Botswana, is nearing
completion.
MINING
INTO AFRICA
...AND BEYOND
