Approaches to Waste Rock Disposal - Mining and the Environment: From Ore to Metal - page 766

siltstones and claystones are susceptible to slaking when wet, causing disintegration and
ultimately reducing the fragment size until the constituent silt or clay particles are released.

Oxidation of Sulphide Minerals

Waste rock containing pyrite and other sulphide minerals is commonly associated with base
metal and gold ore bodies, and coal interburden. Apart from weakening the rock fabric, oxida-
tion of sulphide materials in waste rock may lead to acid rock drainage, which can cause serious
adverse environmental impacts. The rate of oxidation and acid generation varies considerably
from one waste rock type to another, depending on the nature of the sulphide mineralization,
the host rock and the climate. Acid drainage is discussed in detail in Chapter Seventeen.

19.2 POTENTIAL IMPACTS OF WASTE ROCK DISPOSAL

In many mining projects, more environmental damage results from waste rock disposal,
than any other component of the operations. It is also usually the most visible component.
The area occupied by waste rock storages commonly represents a large part of the project
'foot-print', often much more extensive than the mine itself. The most obvious impact is
burial of the land occupied by the waste rock storage, with the loss of values attributable
to that land, whether they be habitat values, agricultural values, or scenic values ( Figure
19.2 ). This does not necessarily constitute a long-term adverse impact as there may be the
opportunity to create conditions on the waste rock storage that represent an improvement
over what was there before.
Storage of unconsolidated waste rock may lead to land-slips, particularly in mountain-
ous areas, in areas subject to high rainfall, and/or in areas of high seismicity. Similarly,
waste rock materials, particularly those containing weak fragments or high fines content,
may be highly erodible. Erosion from waste dumps can lead to major increases in sedi-
ment in downstream streams and rivers, damaging the habitats for aquatic organisms and
potentially affecting use of water for domestic purposes and irrigation ( Case 19.1 ). Of
all impacts caused by waste rock disposal, those involving acid rock drainage are by far
the most serious. There have been many documented cases, some described in Chapter
Seventeen, where large stretches of rivers or streams have been acidified by drainage from
waste rock dumps, resulting in serious reductions in diversity and populations of aquatic
biota and, in some cases, virtually total destruction of aquatic life.

Of all impacts caused by waste
rock disposal, those involving acid
rock drainage are by far the most
serious.

19.3 OBJECTIVES OF WASTE ROCK DISPOSAL

The following objectives apply in planning the storage and disposal of waste rock to mini-
mize environmental damage:
●

The area occupied by the waste rock storage (i.e. its 'foot-print') should be minimized,
in-so-far as this is consistent with other objectives;

●

The new landform created by the waste rock storage should be consistent with its
future land use(s), in terms of slopes, accessibility, surface roughness;

●

The new landform should be stable;

●

The new landform should not be any more erodible than comparable natural land-
forms in the vicinity;