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January 2016
MODERN MINING
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Lift 2 undercut level plan.
The Lift 2 production level.
All time highs
The Lift II project, like its predecessor,
will register among the highest lifts in
block caving. ‘Lift’is the vertical distance
from the production level to the break-
through point on surface or in the open
pit above. Generally speaking, the high-
er the lift, the lower the capital require-
ment per vertical tonne of ore mined.
first block cave conducted in rock of this hard-
ness,” Fouche said. “Our implementation of Lift
II will definitely benefit from that experience.”
One of the issues tackled was the difficulty
in getting sufficient fragmentation from blast-
ing, leading to oversize rocks hanging up in the
drawbells and interrupting smooth production
flows. A range of innovations has resolved this,
including water cannons and medium-reach
rigs to dislodge hang-ups, and robot rigs to drill
and break oversized material.
“For Lift II, we are implementing design
parameters that will optimise fragmentation,”
said Fouche. “We have also modelled different
fragmentation scenarios to prepare the breaking
team for various conditions.”
Continuing its pioneering ways, Palabora’s
Lift II fleet includes the largest Sandvik load-
haul-dumper currently working underground
in Africa – the 12-m, 57-t LH621, boasting a
21-t tramming capacity. This choice makes a
significant difference to the rate of moving rock,
according to Fouche, and has been an impor-
tant contributor to the project to date; apart
from the larger payload, the long wheel-base
enhances grip in muddy and rough conditions.
In a departure from the Lift I configuration, the
new project includes 30-t haul trucks, which
are loaded by the LHDs, to take ore to the
crusher.
In what was probably another ‘first’ for the
operation, the LH621 was transported under-
ground via the vertical service shaft – requiring
the partial dismantling of the vehicle and the
use of a special ‘skeleton’ lift cage to reduce
weight. There are currently three at work in the
project, and there will be about 17 employed in
full production; the question that now remains
is: electric or diesel?
“We are finalising the trade-off between
electric and diesel LHDs,” said Underground
Manager Aidan Schoonbee. “Electric units are
slightly quicker, have a lower life-cycle cost
and generate less heat – but they also have low
predictability given their trailing cables and
the need to move from point to point; they also
need steady-state conditions and mature opera-
tions teams.”
While diesel-powered LHDs offer more
reliability of tonnages, they generate heat and
fumes into an already hot environment: Lift II
will have to deal with virgin rock temperatures
of over 57 deg Celsius.
“The total heat load has been calculated at
30 MW, taking into account cooling and diesel
fumes, should diesel-powered LHDs be used,”
said Schoonbee. “We have three ammonium
refrigeration plants on surface of 6 MW each,
and two chiller plants underground of 3,5 MW
each. Three more 3,5 MW units will be installed
underground.”
Such is the ventilation
challenge at Palabora that
over 30 ventilation passes
have been planned, with two
passes being among the larg-
est in the industry at 6,1 m
diameter and 1 200 m deep
– from the Lift II footprint
to surface. Bored by Master
Drilling’s largest raise borer
yet – its 120-ton SA-designed
RD8 – the shafts benefit from cost, speed and
safety advantages offered by this technology
over the conventional blind-sinking methods.
Connecting the 450-m gap between Lift I
and Lift II are another five large-diameter raises
– three forced-air passes and two return-air
passes. Over 25 shorter raises will be drilled
between the ventilation level and production
level, contributing to better heat management
as well as dust control – an important consid-
eration in the context of underground crushers.
The twin decline also plays a vital ventilation
role, with one decline currently carrying air
down to the workings and the other carrying
air up to surface.
The compound centrifugal chillers at
Palabora are reportedly the first of their kind in
Africa, and the first underground installations