7.9 The use of 'bird balls' at Yatela gold mine, Mali
The area around Yatela mine is home to about 800 species of birds. Although the region once supported a diverse range of large mammal species, these are now relatively scarce due to subsistence hunting. Large expanses of open water, as are common in mining operations, are particularly attractive to both wildlife and domestic animals during the dry season and have to be fenced to keep animals out.
In accordance with company policy, and Malian legislation, an Environmental Impact Assessment (EIA) was carried out for the project. In addition to a description of the existing baseline environmental conditions, the EIA details the likely impact of the various activities. Experiences from the operation of the Sadiola gold mine possibly provided an enhanced confidence in the prediction of the environmental impacts of the Yatela project, but one impact that was clearly not adequately predicted was the effect on birdlife. Soon after the commissioning of Yatela, a number of environmental incidents were recorded at the site. In the first dry season (primarily May and June of 2001), 554 bird fatalities were recorded. This included swifts, swallows, nightjars, buzzards, goshawks and hobbys. Since then a number of measures have been implemented to protect wildlife. The number of bird fatalities decreased to 40 in 2002, 16 in 2003 and to 2 in 2004.
The number of incidents was particularly significant in the dry season, with relatively few incidents in the wet season, when surface water is freely available in natural streams and ponds. As a result of these incidents, a number of measures were put in place to deter birds from frequenting these areas and to reduce their potential expose to cyanide-bearing waters:
- alternative watering points were provided. A series of shallow drinking ponds were constructed around the periphery of the heap leach facility;
- noise deterrents, including the use of propane cannons to emit regular loud bangs, recorded bird alarm calls, and regular patrols were employed to scare away birds;
- to ensure that cyanide-bearing ponding did not occur on top of the heaps, staff were employed to cover ponded areas with shade-cloth, whilst puncturing these surface ponds with long metal rods, to allow the solution to infiltrate into the heap; and
- the solution trenches on either side of the leach pads were covered with shade-cloth, again to prevent birds from accessing this stream of process solution.
On the open water process ponds the most effective solution was found to be the use of 'bird balls'. This technology, which involves floating a large number of HDPE balls on the surface of a pond, effectively covering all exposed water, prevents birds from landing on the water, or perching on the balls. It also disguises the surface of the water ponds, thereby masking the features which birds use to identify water bodies.
Yatela has installed bird balls on its main process solution ponds at a cost of $750,000. A significant contribution to the cost of this solution was due to the remoteness of the operation. Although the mine investigated the on-site manufacture of bird-balls, it was decided to import these with approximately 40 container loads required to provide the number of balls necessary to cover the surface of the process solution ponds.
In the heap leach gold extraction process, cyanide-bearing solution is dripped onto a heap of stacked ore. The solution then percolates through the heap, dissolving and extracting gold as it flows. The solution collects on a HDPE-lined leach pad, and flows into a series of under-drains which flow into solution trenches (on the sides of the heap leach pads) and is ultimately collected in a series of process solution ponds (the barren, intermediate and pregnant solution ponds). The pads and the ponds have been designed and constructed in such a manner to ensure that all cyanide solution is contained within these areas and is not released to the environment. Most of the bird deaths were associated with ponding on the ore heaps, drinking from the solution trenches alongside the heaps and in the open-water process ponds.
The International Cyanide Code in its Standard of Practice 4.4 recommends that measures to protect birds, other wildlife and livestock from adverse effects of cyanide process solutions are implemented for
'all open waters where WAD (weak
acid dissociable) cyanide exceeds
50 milligrammes per litre, such as solution ponded on leach heaps, in leach solution collection ditches and ponds, or in some tailing impoundments'. It stipulates that 'these measures include fencing, filling in collection ditches with gravel, and covering or netting solution in ponds and impound-ments. Fencing is also appropriate in most cases to prevent unauthorised access and potential exposure to humans'.
AngloGold Ashanti is sponsoring and participating in a multi-year project led by the Australian Centre for Mining Extension and Research to investigate the issue of wildlife deaths associated with cyanide-bearing tailings dams and heap leach operations.