dump tailings in Astrolabe Bay
pp. 34-35 · Read in the full issue
Industry
Highlaids Pacific wants ta dump tailings in Astrolabe Bay
By Sam Vulum
THE environmental plan for a major US$B3B mil lion nickel and cobalt mine project in Papua New Guinea has come under close scrutiny.
A Port Moresby-based non-govern ment organisation, the Individual and Community Rights Advocacy Forum (ICRAF), has raised some serious fears of environmental pollution fol lowing the decision by the mine’s developer Highlands Pacific Limited to dump treated tailings into the sea.
This practice is known as Submarine Tailings Discharge (STD) and is now increasingly presented as a safe and viable option by mining com panies.
A discussion paper, commissioned by the Mineral Policy Institute of Sydney, Australia in February 1999 in consultation with ICRAF - high lighted several environmental risks associated with STD in Astrolabe Bay, in the Madang Province where the tailings are expected to be deposited.
MPI commissioned the scientific report in response to concerns raised by community groups, including the
Icraf, In Png.
It examines the environmental risks which arise from the proposed STD into the Astrolabe bay.
The government is yet to decide on the environmental plan, although its initial reactions were favourable.
The report is a pre-requisite of a special mining lease for the project.
Highlands Pacific Limited said in the environmental plan - now before the PNG government for consideration - that a total of 100 million tonnes of treated tailings will be released over a I
20-year project life of the mine, via a pipeline into the sea.
The company’s managing director, lan Holzberger said the project would be a unique mine in PNG because it will not leave a hole in the ground, no tailings dam will be required and mined areas will be re-vegetated
immediately.
Holzberger said the rehabilitation plan will be put into action as the mine goes into operation.
He said ore will be mined in cells of one to four hectares by excavators, and hauled by trucks to a “benefica tion” plant.
Rehabilitation will start as soon as a cell is mined.
Top soil, or overburden, which was earlier moved along with the vegeta tion, will be returned to previously mined surfaces for revegetation.
After the ore becomes slurry at the benefication plant, it will be piped into a refinery. The material will be processed into one metre by one metre sheets of nickel and cobalt, ready for export to stainless steel manufactur ers.
Holzberger said this makes the Ramu project the first minerals project to set up a processing plant in PNG.
According to the environmental plan, the tailings will be treated, acid contents neutralised and soluble metal contents extracted before disposal.
The outlet of the pipeline is planned for 150 metres below the deepest measured zone of sunlight (euphotic zone), 50 metres below the zone where upwelling can occur and 30 metres below the deepest measured surface mixed layer of the ocean (where wind and wave action mix and
circulate freely).
The location of the outlet will be in
a steep-sided submarine canyon that will direct the flow of tailings into a deep ocean basin.
The tailings’ material will consist of treated alkaline slurry from which nickel and cobalt have been removed.
The tailings will flow by gravity pipeline from the refinery which will be located on the coastline and into a tailings’ disposal tank for a neutralisa tion process before it travels by sub marine pipeline to the 150-metre depth of release.
The MPI report acknowledges that the direct disposal of mine tailings into the ocean has been practiced in parts of the northern hemisphere for more than 50 years.
It says that it is only in the last 25 years with the increase in environmen tal awareness and closer regulation that mining companies have attempted to place tailings at depths below the well-mixed surface zone to mitigate adverse environmental effects.
Recently new mines in the region have tended to discharge tailings at a
depth of around 80-100 m although
some mines in the Indonesia/PNG region discharge below this level.
It also acknowledges that STD has recently come into favour in PNG where on-land disposal options are
problematic.
Two mines, Misima and Lihir, use
this technique.
According to the report, STD is an attractive option for PNG for several reasons. In comparison with on-land tailings retention, it is arguably safer both to local people and the environ ment.
It accepted that much of PNG is unsuited to the construction of tailings dams due to rugged topography, seis mic activity and rainfall.
These factors increase the likeli hood of a disastrous dam failure. As tailings require continuous monitor ing and post-mine remediation, STD is also cheaper in the long term.
However, the MPI report says that in practice, it is inevitable that STD operations will have adverse effects in the receiving environment.
All STD operations around the world cause increases in suspended sediment, trace metals and residual milling reagent concentrations in the receiving waters.
These components of the tailings can detrimentally affect or alter ben thic invertebrates and fish, pelagic zooplankton and fish, and the phyto plankton and microbiota on which these animals rely.
The repo.rt also attempts to show that the Misima and Lihir mines, which also use the STD technique, should not be compared with the Ramu nickel and cobalt project.
The report says both mines have receiving slopes that are far steeper than those in Astrolabe Bay.
According to the report, submarine tailings discharge generally form a coherent density current on the seabed which transports the solids under the influence of gravity at greater depths.
It says deposition from these den sity currents generally occur on seabed slopes less than 12 degrees.
In Astrolabe Bay, these low slopes are reached at a depth of about 250 m, and by 300 m depth the slope is on average only 3 degrees.
It is therefore highly likely that substantial quantities of tailings’ material will be deposited in the vicinity of 300 m depth, and will not be transported as a coherent flow of abyssal zones.
Further, the report said the are within the 100-300 metre zone is sub ject to the permanent movement of the New Guinean Coastal Undercurrent (NGCU) that carries water along the New Guinean coast.
The report says it is highly likely that this current will carry with it tail ings’ material and transport it to the West.
While it is expected that tailings material will be rapidly diluted after
its entrainment in the NGCU, on the basis of other STD case histories, one could expect high concentrations of tailings to be found in these waters for a considerable distance to the north west of the site.
During the NW monsoon, this water body, through its interaction with opposing surface currents, upwells along the coast.
Consequently it is probable that tailings will be brought to the surface of the Astrolabe Bay coastline during the monsoon period.
It this occurs, it will have a signif icant impact on the productivity and ecology of Astrolabe Bay and the Madang coastline.
MPI was established in 1995 to address the rapidly increasing impact of minerals development world-wide, and specifically, the impacts of Australian minerals companies in the Asia Pacific region.
It is a research and advocacy organisation based in Sydney, Australia. The history of the project goes back to the 19605.
A lateritic nickel deposit was dis covered at Kurumbakari, a site of the Ramu river, in the early 19605.
It was owned by a succession of interests before it was taken up by Highlands gold in 1993.
In 1997, the Highlands Pacific Limited group, through its wholly owned subsidiary Ramu Nikel Limited, acquired Highlands Gold’s 65 per cent interest in the project and became manager of the Ramu Joint Venture.
A feasibility study indicating the technical and commercial viability has been completed and Highlands Pacific are currently seeking financial backing to allow the project to start in mid this year.
Natural Systems Research of Hawthorn, Australia was commis sioned by Highlands Pacific to pre pare the environmental report.
It has been projected that the Ramu mine will generate between US$26O million to US$27O million in revenue annually. The mine is expected to employ 2500 people at peak construc tion period and maintain a workforce of 1045 during operations. ■