Mine Closure - Mining and the Environment: From Ore to Metal - page 802

TABLE 21.1
Post-Mining Risks and Hazard Reduction Measures - Risks associated with abandoned mine sites vary widely and are many

Mine Component Type of Risk Management Measures

Open pit Collapse or slides due to unstable walls Usually a combination of:

Accumulation of deep water, possibly of poor quality Warning signs,

Fences and/or abandonment berms,
Flattening of batters and highwalls, and less often,
Back-fi lling - partial or complete.

Shaft, tunnel or adit Collapse Usually a combination of:

Entry point to underground workings that may be unsta-
ble, fl ooded or poorly ventilated

Warning signs,
Fences and/or abandonment berms,
Capping of shafts,
Back-fi lling of shafts - partial or complete.
Installation of barricades, locked gates or bulkheads at or
inside the portals of tunnels or adits.

Tailings impoundment Collapse or overfl ow due to fl ooding or blockage of

spillway,

Combination of:
Warning signs,

Boggy surface could trap human visitors or livestock, Fences,

Removal of water and establishment of surface drainage system,
Establishment and maintenance of adequate spillway capacity.

Waste rock dumps Landslips Shaping to form stable profi le.

Mill and processing plant, plus
ancillary facilities

Becoming unsafe over time, if abandoned. Decommissioning,

Dis-assembly, and
Removal

Source:
Khanna 2000

assurance - either imposed on operators by legislation, negotiated in project-specii c agree-
ments or as voluntary commitments. These instruments include: third party agreements,
cash deposits, letters of credit, trust funds, insurance policies and corporate guarantees
based on a pledge of assets. The advantages and disadvantages of each are listed in Table
21.2 , which has been reproduced from Fleury and Parsons (2006).
It is common for the amount covered by a i nancial assurance instrument to change
regularly in response to revised calculations of closure liabilities. In some cases involving
cash deposits, trust funds or balance sheet entries, the funds are accrued progressively in
accordance with an agreed schedule, for example per unit of product or per unit of area
disturbed. Similarly, accrued funds can be reduced as various closure tasks are complete as
coni rmed by the achievement of pre-arranged performance criteria.
It is evident that performance guarantees have been devised mainly to protect against
default by small and medium operators, who have been responsible for the vast major-
ity of inadequate closure efforts in the past. Companies with strong balance sheets and,
in particular, companies with multiple operations, are much less likely to default. A good
example of this is the unplanned closure of the Marcopper Mine in the Philippines fol-
lowing a major tailings discharge (Case 18.1). Here, the part owner and operator, Placer
Pacii c, accepted responsibility for remediation, reportedly spending more than $ 40 mil-
lion in clean-up costs. It follows that balance sheet provisions may be sufi cient in the case
of such companies, whereas for a small company, a balance sheet entry may provide little
protection for the host country.

The amount covered by a
fi nancial assurance instrument
is changed regularly in response
to revised calculations of closure
liabilities.