Tailings Disposal - Mining and the Environment: From Ore to Metal - page 718

Objectives of Tailings Storage
The overall goal of a tailings storage facility is to provide secure containment for tailings
during operation and, following closure, to retain its integrity in perpetuity. This is not
easily achieved, and it is evident that many older tailings storages fall short of this goal. In
planning tailings storage facilities, common objectives are to:
●

Minimize the footprint of the facility, consistent with other requirements;

●

Design and construct retention structures that are stable under all foreseeable condi-
tions, with an adequate factor of safety to protect against uncertainties;

●

Provide sufi cient freeboard and manage the facility so as to accommodate inl ow from
the maximum credible operating and rainfall scenarios;

●

Minimize, and in some cases intercept and recover, seepage through the base of the
storage area and/or beneath the retention structure;

CASE 18.2
Riverine Tailings Disposal of Freeport's Grasberg Copper and
Gold Mine in Papua, East Indonesia

be jeopardized by natural events such as landslides, fl oods
and earthquakes.
Tailings enter the river system at rates exceeding
200,000 tonnes per day. While the majority of the tail-
ings is captured in the designated tailings deposition area,
tailings fi nes freely enter the Arafura Sea. The riverine
tailings disposal scheme is accompanied by a comprehen-
sive environmental monitoring programme (in 2005, water
quality was monitored at over 300 locations throughout
the project area, collecting over 7,000 water samples
and conducting over 50,000 water quality analyses; and
monitoring more than 100 sampling locations for nekton,
benthos, plankton and mangrove invertebrates in the
aquatic biology programme).
Freeport's riverine transport of tailings differs from the
riverine disposal by the Ok Tedi mine in nearby Papua
New Guinea in three main respects. First, the OK Tedi mine
uses the river system for tailings and waste rock disposal.
Second, at Ok Tedi, mine tailings transport occurs over 990
kilometres along the Fly River compared to river transport
by the Aikwa River over 80 kilometres. Using hydraulic
jargon, the transport capacity of the Ajkwa is much
greater. Finally, the Freeport deposition area in the low-
lands is laterally confi ned by a levee system. Only time will
tell, however, whether such large-scale tailings management
systems can be successfully managed over many decades
and adequately rehabilitated.

The high-mountain Grasberg mine site lies near the collision
point of two tectonic plates - the Indo-Australian plate to
the south and the Pacifi c plate to the north. The open Pit
mine is located close to the highest point on the island at
an elevation of more than 4,000 metres above sea level.
Ore containing copper, gold and silver is sent to a mill/
concentrator facility in a valley about three kilometres to
the south and approximately 1,000 metres lower in elevation,
where the mineral-bearing material is separated from non-
economic rock material through a physical separation process
by grinding and fl otation methods. A pipeline sends metals
bearing concentrate to the port facility near the Arafura Sea,
approximately 120 kilometres to the south. Freeport uses
the Aikwa river system for tailings transport to a designated
area in the lowlands and coastal zone, called the 'Modifi ed
Deposition Area'. The deposition area is a portion of the
fl oodplain of the river, confi ned laterally by a levee on each
side, encompassing some 235 square kilometres. When mining
is completed, it is envisioned that the deposition area which
by then will rise up to 30 metres above the surrounding
ground, will be reclaimed with natural vegetation or used for
agriculture, forestry or aquaculture.
Alternative tailings storage areas were rejected due to
lack of capacity or the necessity of building an extremely
high dam in a seismically active area with high amounts
of precipitation. The use of a pipeline to carry tailings to
the deposition area was also rejected because construc-
tion and installation of a large diameter pipeline in a
harsh terrain over such a long distance had never been
attempted before. The integrity of the pipeline would likely

Source: Based on Riverine Tailings Transport by PT Freeport
Indonesia (2006)