Tailings Disposal - Mining and the Environment: From Ore to Metal - page 754

Mix/
De-aeration
Tank

Thickener

Beach and Surf
Zone

Active Mixing
Zone

HDPE
Pipeline

Seawater
Intake

Surface Mixed Zone

Steel
Pipeline

Euphotic Zone

Burried
Pipelines

Tailings
Discharge
Pipeline
Placed on
Seabed

Deep-Sea Zone

Concrete
Saddle
Weights

Tailings Outfall
Below Euphotic Zone

18.5 COMPLETED AND OPERATING STP PROJECTS

FIGURE 18.18
Typical DSTP Arrangement

Table 18.8 lists some examples of early STD projects which are now complete. These early
STD projects provided much of the design data and operating experience on which sub-
sequent systems have been based. As in most new technologies, the i rst examples expe-
rienced unforeseen problems, leading to safeguards being incorporated into subsequent
designs. Some examples follow.
The Island Copper Project pioneered many of the concepts that have since been incor-
porated in other projects. A comprehensive marine monitoring programme was conducted
throughout operations and following closure, providing an invaluable long-term record
of impacts and post-closure recovery. Remarkably, this project operated for a very long
period and discharged hundreds of millions of tonnes of tailings, without affecting com-
mercial salmon and crab i sheries in the vicinity, despite the fact that, by today's standards,
the tailings were discharged and accumulated in shallow water.
The Atlas Copper Project was another early pioneer of STD. The sub-sea outfall was
located on a tower founded on the seabed. After many years of successful operation, the
tower was destroyed by a typhoon. Subsequent STD installations at other sites have used
pipelines buried through the beach and surf zones and anchored to the seabed by saddle
weights, thereby avoiding damage during typhoons.
Blockage of the outfall of the Minahasa STD outfall occurred during a plant shutdown.
This led to the practice of maintaining water discharge through the pipeline during plant
shutdowns. Subsequent STD designs have involved discharge where seabed slopes are suf-
i ciently steep that the tailings slurry l ows well away from the outfall.
The submarine landslide that severed the subsea tailings pipeline at Misima has led, in
such steeply sloping areas, to implementation of geophysical investigations to help identify
stable areas for the pipeline route.
Table 18.9 lists examples of DSTP systems, in operation as of 2006. These include the
Lihir and Batu Hijau systems which are the most recent examples and which include safe-
guards based on incidents that occurred at previous operations. Case 18.6 provides a criti-
cal comparison of the Batu Hijau DSTP scheme with the tailings disposal schemes of three
other large mines developed in similar environmental settings.

The euphotic layer is defi ned as the
depth reached by only 1% of the
photosynthetically active light transmit-
ted from the ocean surface.
Source: MMSD 2001 and Jones and Jones 2001