Tailings Disposal - Mining and the Environment: From Ore to Metal - page 721

boundaries. The natural river system transports tailings to the i nal resting place which is
not entirely dei ned. Hence, the extent of the impact remains uncertain.
While land-based tailings storage schemes are readily accepted and submarine tailings
placement schemes, although controversial, have also proved to be environmentally accept-
able, riverine disposal of tailings, although practised throughout mining history is now
considered unacceptable by most authorities. At present, only a few mines, all located in
the Asia Pacii c region, rely on this practice: the OK Tedi Copper Mine, the Porgera Gold
Mine and the Tol Okama Gold Mine, all located in Papua New Guinea; and Freeport's
Grasberg Gold and Copper Mine in Papua, Indonesia ( Case 18.2 ).
In all current cases of riverine tailings disposal, specii c conditions at the mine site dic-
tated riverine tailings disposal. At Ok Tedi, riverine disposal became the default option
when a foundation failure occurred during construction of the TSF. On-land tailings
storage close to the Freeport's Grasberg mine, located high up in steep mountain terrain,
would be physically impossible and tailings transportation via pipeline to the lowlands
over long distance and inaccessible terrain has never been attempted.
Environmental impacts on river systems due to tailings disposal are complex. The obvi-
ous impacts are related to very high suspended sediment loads and deposition of sediments
in downstream areas, including the seabed. In these respects, the impacts are similar to
those resulting from glacial rivers such as many in Alaska. The difference is that the eco-
systems in glacial areas, have adapted to the high sediment loads over millennia. Coarse
materials deposit closer to the discharge point. Fine tailings are easily transported through
the entire river system, eventually reaching the coastal environment. In both the Freeport
Copper Project in Indonesia and the Ok Tedi Copper Project in PNG, the quantities of
discharged tailings have exceeded the transportation capacities of the rivers in their down-
stream reaches, causing aggradation and eventual bank overl ow. In both cases, wide-
spread loss of forest vegetation has resulted from sediment accumulation in forest areas
outside the river channels. In the case of Ok Tedi, riverbed levels increased by up to 6 m.
In case of the Freeport mine where levees have been constructed to coni ne deposition, the
surface of the tailings deposition area is predicted to rise by up to 30 m. Tailings i nes, how-
ever, freely enter the Arafura Sea. Trace metals are a concern in riverine tailings disposal
systems, with the potential for geochemical changes by which metals may dissolve or pre-
cipitate at different distances from the discharge point, due to oxidation, reduction, dilu-
tion or other processes. Acid drainage may occur if the tailings contain sulphide minerals.
Today, riverine tailings disposal is only used for a few large mines where there is no
practicable alternative and which are economically too attractive to both the host country
and the mine developer, to remain undeveloped. While it can be argued that the major
economic benei ts provided by these mega-projects outweigh the environmental costs, it is
unlikely that projects involving riverine disposal will ever be permitted in the future.

Today, riverine tailings disposal is
only used for a few large mines
where there is no practicable
alternative and which are
economically too attractive
to both the host country and
the mine developer, to remain
undeveloped.

Surface Tailings Storage

Surface or on-land tailings storage is used by the vast majority of mining operations. In some
cases tailings are stored in underground openings or surface pits but, more commonly, the tail-
ings are deposited in purpose built containment facilities or impoundments. Most established
mining companies, wherever possible and practical, prefer to store tailings in engineered tail-
ings storage impoundments. Accordingly, tailings solids are coni ned within well-dei ned areas.
In some cases the tailings of today could be the ores of tomorrow if advances in extraction tech-
nologies allow further tailings processing to be economically attractive. However, advances in
recovery rates mean that such cases are likely to be less common in the future than in the past.

In some cases the tailings of
today could be the ores of
tomorrow.