Sustainability Report - Antofagasta PLC

Mining waste
Antofagasta Minerals carefully manages mining waste to reduce the amount
of waste produced and safely dispose of it according to legal requirements.
At Michilla and El Tesoro where leaching is used to extract copper, each
operation designs and maintains special storage facilities for waste gravel
that are authorised by the Chilean environmental authorities.
Los Pelambres has a range of measures in place to ensure the safety of
inhabitants near to tailings facilities and protect local water courses from
leaching of heavy metals or sulphates. Its Quillayes dam is no longer in use
and it has established a larger dam at El Mauro. Both dams are built to
resist extreme weather, such as flooding and high-magnitude earthquakes,
and are carefully monitored and maintained. Safety features are built into
their construction to prevent accidental release of tailings into both surface
and underground water courses. The pipeline to Los Pelambres’ El Mauro
Dam includes overflow ponds to prevent leaks. At Quillayes, the Cuncumén
River was diverted through a tunnel to keep its water from mixing with the
dam’s waters. We are piloting an environmental remediation plan known as
phytostabilisation for the closure of the old tailings dam. We aim to cover
400 hectares with top soil and then plant it with species which will reduce
the risk of contamination and leaching.
See page 45.
Mining waste management (million tonnes)
CONCENTRATION dEPOSITS
Los Pelambres
Esperanza
LEACHING dEPOSITS
El Tesoro
Michilla
Total
Total mining waste
(waste rock, tailings &
gravel)
Waste rock
60.0
61.2
54.2
6.0
181.5
2011
Tailings
63.3
20.0
n/a
n/a
83.2
279
* Esperanza began a ramp-up for its operation in the last quarter of 2010.
Gravel
n/a
n/a
9.7
4.6
14.3
Antofagasta Minerals 57
Taking advantage of its geographical location, Esperanza has developed a
thickened tailings deposit, one of the largest in the world. This reduces water
consumption and the risk of soil contamination, and means that tailings are more
stable during operations and after the mine has closed. It also reduces dust
levels. This is an innovation never used at such scale before and its operation
has presented challenges as the tailings system has not performed exactly
according to design at the actual processing rate. In response, Esperanza has
developed and submitted a contingency plan to the environmental authorities.
The mining companies have groundwater and surface water monitoring systems
in place to ensure that water quality or flow is not affected. At Los Pelambres,
the quality of the water is monitored at several points throughout the valley and
the measurements are published annually on www.pelambres.cl. Water quality is
also monitored at Esperanza’s tailings facility, although the facility is located in
the desert where no underground water sources have been identified.
In 2011, the total volume of mining waste (waste rock, tailings and gravel)
produced at our operations increased by 11.5% from 2010 levels, due to
Esperanza’s first full year of operation.
Waste rock
67.4
39.7
66.0
5.1
178.2
2010
Tailings
57.4
n/a*
n/a
n/a
57.4
250.3
Gravel
n/a
n/a
9.4
5.4
14.8
Waste rock
79.5
37.4
34.0
0.0
151.7
2009
Tailings
46.2
n/a
n/a
n/a
46.2
214.2
Gravel
n/a
n/a
10.9
5.4
16.3
Overview
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