Approaches to Waste Rock Disposal - Mining and the Environment: From Ore to Metal - page 768

● The design of the storage; in particular the need for encapsulation of sulphidic materi-
als, or incorporation of elaborate drainage provisions;
● The method of construction, including foundation preparation; whether 'top-down'
or 'bottom-up' ( Figure 19.3 ); compacted or uncompacted; and the extent of regrading
required to achieve the final surface configuration.
From an environmental view-point, the best possible sites for storage of waste rock are
mined-out areas. Burial of mine wastes below the original ground surface is known as
below-grade storage, as opposed to above-grade storage as is the case where wastes are
stored above the natural ground surface. Below grade storage of waste rock is achieved rou-
tinely in the case of strip mines for coal, and is also common in extensive shallow surface
mines such as those for the extraction of bauxite and lateritic nickel ores. It is also being
used increasingly in open Pit gold mines where multiple but discrete ore bodies occur in
close proximity. The advantages of using waste rock to fill mine voids may include:
● Minimizing the foot-print and, in particular, the 'residual foot-print', which is the land
disturbance that remains after the completion of rehabilitation;
● Stabilizing the void. Many surface mines have unstable slopes or slopes that may
become unstable over time;
● Isolation of potential acid-generating wastes. The best possible site for such wastes is
below the water table, and many mine voids provide such sites. However, even if the
void does not extend below the water table, the storage of potential acid-generating
waste below grade is far preferable to storage above grade, as the chances of acid drain-
age reaching the surface are much reduced.
If below grade storage is not feasible, the next best option, in terms of minimizing the
foot-print, is to utilize one or more natural depressions in the landscape. In mountainous
terrain, filling or partially filling a valley, may represent the only realistic option available

From an environmental
view-point, the best possible sites
for storage of waste rock are
mined-out areas.

CASE 19.1
Adverse Agricultural Effects from Mines in Northern Luzon, Philippines

The Cordillera region of Northern Luzon in the Philippines
has long been the location of gold mining activity. During
a period of high mineral production in the Philippines
in the 1970s and early 1980s, prior to the introduction
of environmental controls, uncontrolled dumping of waste
rock and tailings, contributed large quantities of sediment
to the Abra River which drains from the mountains across
the coastal plain to the South China Sea (see photo).
Accumulation of this sediment in the river channels led to
bank overfl ow during the wet seasons, so that sediment
composed largely of mine waste became widely distributed
over the fl ood plain, clogging irrigation ditches and deposit-
ing on paddy fi elds. Adverse impacts included lower crop
yields due to the low fertility of the mine-derived sedi-
ment and high costs for maintenance of irrigation systems.
Consequent unrest among the agricultural communities
contributed to the eventual strengthening of environmental
legislation relating to mining in the Philippines.