OVERBURDEN AND ACID ROCK DRAINAGE
MANAGEMENT
Overburden is rock that must be moved aside to gain access to ore
that is mined and processed to produce metals for commercial
purposes. PT Freeport Indonesia handles overburden under a
comprehensive Overburden Management Plan approved by the
Government of Indonesia. Most metals occur in nature as sulphide
minerals. When ore is mined and overburden containing sulphides is
left exposed to the elements, the action of water, oxygen and
natural bacteria has the potential to create sulphuric acid. This
acidic water can dissolve metals contained in overburden rock and
be transported in water drainage systems and, if not properly
managed, cause adverse environmental impacts. This process is
known as acid rock drainage.
PT Freeport Indonesia manages and monitors acid rock drainage from
its operations. Independent audits of PT Freeport Indonesia's
environmental management system concluded that our overburden
management programs are "…consistent with international practice."
Under the Government-approved overburden management plan, PT
Freeport Indonesia places overburden in managed areas around the
Grasberg open pit.
PT Freeport Indonesia's acid rock drainage mitigation plans
provide for capture and treatment of the existing acid rock
drainage, in conjunction with limestone blending and limestone
capping of existing overburden placement areas. These actions are
expected to significantly reduce future acid rock drainage
generation. Throughout 2003, acid rock drainage from the mine was
captured and transported via a system of pipes to the mill for
lime neutralization. |
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Native highlands
species
of grasses, mosses and shrubs are successfully grown on
overburden placement areas. Overburden sites and the open pit
will be revegetated or reclaimed after the end of mine-life. |
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