Acid Rock Drainage - Mining and the Environment: From Ore to Metal - page 686

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Acid Rock Drainage

A Widespread Problem

Many of the most diffi cult and expensive environmental problems faced by
mining companies result from Acid Rock Drainage (ARD). Sulphide minerals such
as pyrite and pyrrhotite are commonly associated with many ore types, and it is
the oxidation of these minerals and subsequent leaching of their acidic oxidation
products including sulphuric acid, that leads to ARD. Discharge of acid solutions from
mine workings is usually known as Acid Mine Drainage (AMD). As if generation of
acid itself is not of suffi cient concern, the potential for widespread and possibly far-
reaching environmental damage is aggravated in many situations, by the presence of
'heavy metals' such as manganese, copper, arsenic, and zinc which may dissolve in
acidic solutions, thereby becoming mobilized and, potentially, 'bio-available'.

There is the potential for ARD to develop at most operations in which the ores or sur-
rounding waste rocks contain sulphide minerals such as pyrite. Examples of such opera-
tions include most gold mines, most major copper mines and many mines producing
silver, lead, zinc, or nickel. Many coal mines are also subject to ARD, due to the presence
of pyrite within the coal, overburden, or interburden. ARD is not associated with projects
where only oxidized ores are mined. These include lateritic mining operations for bauxite
or nickel, iron and manganese mines, and many near-surface gold and copper operations.
Some uranium deposits are associated with sulphide minerals (e.g. the Rum Jungle deposit
in Australia's Northern Territory), while others are not.
ARD may occur in or may be derived from many parts of an operation, including:

There is the potential for ARD
to develop at most operations
in which the ores or surrounding
waste rocks contain sulphide
minerals such as pyrite.

●

Runoff from surface excavations for access roads, drains, and site facilities;

●

Drainage or seepage from underground excavations for mine access, exploration,
development, ventilation, and extraction;

●

Runoff from open pit mines - exposures in pit walls, berms, and the mine l oor;

●

Seepages of contaminated groundwater into surface or underground mines;

●

Percolation through and drainage from rock masses fragmented by block caving or
subsidence;