Mine excursion
carbon in pulp (CIP) circuit for recovery
of gold in solution. The tailings stream
from the CIP circuit is treated in a cyanide
destruction circuit using the sulphur
dioxide/air process, before being pumped
to a lined tailings storage facility. Gold is
recovered in the CIP circuit by loading
it onto carbon, and the loaded carbon is
sent to a split Anglo-American Research
Laboratories (AARL) elution circuit. Gold
solutions from the gravity-intensive leach
circuit and elution circuit are treated in
an electro-winning process, followed by
smelting to produce doré bars.
“The bottom line is that each mine has
to adapt its processing plant according to
what it has in the ground,” says Barnard.
“B2Gold’s plant at Fekola in Mali also
runs at high recoveries, although they have
a grade of about 2 grams per tonne. The
major difference is that Fekola doesn’t have
a gravity circuit. The plant has a different
design because the ore body it treats is
completely different,” Barnard adds.
Mining in phases
“We started mining ore from the Otjikoto
Pit. That was Phase 1. While we were
mining at Otjikoto, we started with the
stripping at Wolfshag, the other pit. As
soon as the pushback at Otjikoto got
under way during what we call Phase 2,
mining of the Wolfshag ore body was
initiated. It is an alternate cycle to ensure
we have a continuous supply of ore to
feed the processing plant. In 2018, we
have been mining at Otjikoto Phase 2,
while stripping at Wolfshag Phase 2,”
explains Mawoyo.
Mawoyo says the two biggest challenges
in the pit are managing the complexity of
the operation and reaching the daily target
of 106 000 tonnes per day from both pits,
which includes ore and waste. “We have
to keep the equipment running, and the
utilisation of the equipment has to be
high for us to achieve those tonnages. At
the moment, we have an 86% availability
on the trucks. It will become a challenge
though as we mine deeper and the
equipment starts getting older. Moreover,
the cycle times will also start increasing as
we go deeper and as the dumps increase in
size,” says Mawoyo.
“Otjikoto uses conventional open-pit
mining methods and is a fully owner-
mined operation,” says Dawe and explains
that the first phase of the mining cycle
at Otjikoto is grade control drilling and
sampling. “This is to better identify known
ore zones and to develop ore polygons
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Equipment used in the mine
Production drills
2 × DK25 Sandvik
3 × MD6240 Caterpillar
1 × MD6290 Caterpillar
Wall control drills
2 × MD5125
1 × MD5150
Haul trucks
18 × Caterpillar 100t 777D
5 × Caterpillar 100t 777E
Hydraulic face shovels
(waste stripping only)
2 × Caterpillar 6018
Hydraulic excavators
(mainly ore loading)
2 × Liebherr 9250
1 × Liebherr 984
Wheel loaders
(waste stripping and crusher feed)
1 × Caterpillar 992
2 × Caterpillar 990
that will aid in the selective mining of the
ore body once blasted,” he says.
After grade control drilling is
completed, conventional blasthole rigs
drill systematic blast patterns that are
then charged and blasted. The blasted ore
and waste are mined separately by large
hydraulic excavators into awaiting 100-ton
haul trucks. The trucks haul the blasted ore to the appropriate ore stockpiles in
preparation for milling; blasted waste goes
to its respective waste dumps.
With the blasted ore and waste
removed, the mining cycle can start over
again with the required grade control
drilling. “This continuous mining cycle
will be used at Otjikoto to efficiently
mine both ore and waste,” says Dawe.
Otjikoto’s performance in 2018 higher-than-budgeted production and
lower general and administrative costs and
were lower than the prior-year quarter due
to lower capital expenditures for mobile
equipment purchases.
Year-to-date, gold production at the
Otjikoto Mine was 122 580 ounces of gold
(year-to-date 2017 – 139 088 ounces),
above budget by 3% (4 027 ounces). For
the first nine months of 2018, Otjikoto’s
cash operating costs were USD514 per
ounce (year-to-date 2017 – USD459 per
ounce), USD19 per ounce (4%) below
budget, and AISC were USD747 per
ounce (year-to-date 2017 – USD756 per
ounce), USD15 per ounce (2%) below
budget. Capital expenditures in the third
quarter of 2018 totaled USD12-million,
mainly consisting of USD6-million for
pre-stripping, USD3-million for new
equipment, and USD1-million in mobile
equipment rebuilds. Capital expenditures
for the nine months ended 30 September
2018 totaled USD41-million, mainly
consisting of USD21-million for pre-
stripping, USD10-million in mobile
equipment rebuilds, and USD4-million for
the new solar power plant.
For full-year 2018, the Otjikoto Mine is
expected to produce between 160 000 and
170 000 ounces of gold, primarily from
the Otjikoto Pit, at cash operating costs
of between USD480 and USD525 per
ounce and AISC of between USD700 and
USD750 per ounce.
Otjikoto delivered another quarter of solid
production, producing 42 403 ounces of
gold in the third quarter of 2018. This
exceeded budget by 4% (1 568 ounces),
mainly due to higher-than-expected mill
throughput (870 125 tonnes compared
to budget of 831 781 tonnes and 873 516
tonnes in the third quarter of 2017).
Mill recoveries also remained high and
averaged 98.7%, exceeding both budget of
98.0% and 98.5% in the third quarter of
2017. Compared to the prior-year quarter,
gold production was lower by 23% (12 748
ounces), as planned, due to a negligible
amount of Wolfshag ore being mined
in 2018 while Phase 2 of the Wolfshag
Pit is being developed. Higher-grade ore
production is planned to resume from the
Wolfshag Pit in late 2019. As a result, the
average grade processed in the quarter was
1.54 grams per tonne (g/t), compared to
budget of 1.52g/t and 1.99g/t in the third
quarter of 2017.
For third quarter 2018, Otjikoto's
cash operating costs were USD470 per
ounce (Q3 2017 – USD447 per ounce),
USD14 per ounce (3%) below budget,
mainly the result of higher-than-budgeted
production. Otjikoto’s all-in sustaining
costs (AISC) were USD662 per ounce,
well below budget by USD53 per ounce
(7%) and USD147 per ounce (18%) lower
than the prior-year quarter. Otjikoto’s
AISC were below budget mainly due to
FEBRUARY 2019 MINING MIRROR [21]