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July 2015
MODERN MINING
29
feature
COUNTRY FOCUS –
BOTSWANA
The XRT building houses five
high-capacity Tomra XRT
machines.
Left:
The coarse
(14 – 32 mm) XRT feed
fraction.
Right:
These
four stones of 270 ct,
196 ct, 142 ct and 342 ct
were recently recovered
at Karowe. The 342 ct
diamond was recovered
prior to the commissioning
of the XRT machines but
the others represent the
first significant recoveries
from the XRT circuit.
to allow it to treat harder and higher yield
material, particularly in the south lobe of the
kimberlite, and its design allowed for this,” he
explains. “As it became clear, however, that the
mine was emerging as a prodigious producer of
large diamonds, we decided that we would also
need to incorporate a facility to avoid breakage
of large stones and allow Lucara to realise their
full value. So the entire project has had two ele-
ments to it – the upgrade, which was always
planned, and a ‘Large Diamond Recovery’ cir-
cuit able to treat material up to 60 mm in size.”
To cater for both the anticipated increase
in DMS yield and assist with the recovery of
large stones, Lucara elected not to increase the
DMS capacity, but to go for new technology
that represents a ‘first’ in the diamond mining
industry – the use of X-ray Transmission (XRT)
machines. The selection of XRT was based on
extensive testwork on the Karowe ore which
indicated that the XRT route was superior to
other concentration methods examined.
The entire upgrade and optimisation project
at Karowe was covered in our January issue this
year but, to briefly recap, the work – carried out
by DRA as EPCM contractor – has encompassed
modifications to the autogenous mill (which,
incidentally, was the first mill of its type to be
installed at a diamond mine in Africa outside
of Angola), the installation of new secondary
and tertiary crushers, and the construction of
an XRT building housing five high-capacity
Tomra XRT machines.
The process route for all ore now is for the
+1,5 x 8 mm ore fraction to go to DMS and
XRF (X-ray Fluorescence) recovery with the