Environment

Printer friendly

At Bibiani mine, as at all AngloGold Ashanti mines, water conservation and the prevention of polluted discharges into the environment are important aspects of water management. The mine is located close to the River Mensin and its tributaries, the Mpokwampa and Amponsah streams. At a slightly greater distance lies the river Tano, one of Ghana’s major rivers into which the River Mensin flows. A number of communities are located within the mining lease area, and also beyond its boundary. They rely mainly on streams and shallow wells for their domestic water supply.

At the mine’s tailings dam, the repository for slurry after the gold extraction process, all of the mine’s water is recycled as part of the mine’s zero effluent discharge philosophy, which means that process water is contained in a closed system and that there is no seepage or spillage of water into the environment. This water management programme has been in place since the mine was re-started as an open-pit mine in 1998, prior to which it was an underground operation for many decades.

At Bibiani, water is used in the milling and chemical extraction process in the treatment of approximately 2.5 million tons of ore annually. The ore is crushed and milled prior to leaching by cyanidation. The gold is then absorbed (collected) out of solution onto activated carbon and the residual solution is recycled to the process plant as process water.

Bibiani’s water supply is obtained from a number of sources:

• the mine’s tailings dam;
• levees (raised embankments for water storage) – the mine has five levees which store rainfall, underground water and, on a temporary basis, water from Lake Amponsah, until the water is pumped to the process plant;
• dewatering from the mine’s underground project; and
• Lake Amponsah (water from the lake is used only when other sources are inadequate).

Bibiani’s total water consumption for 2005 was estimated at 3.5 million m³, almost 76% of which was recycled water. This meant a saving of 2.3 million m³ in fresh water abstraction.

The water from the tailings dam, which forms the bulk of the water source, is recycled for re-use at the process plant. Waste from the treatment process forms slurry which is pumped to the tailings dam or tailings storage facility (TSF). The quality of the water is then improved through a decanting process which consists of both a particulate and a liquid phase: metal pollutants like iron and manganese settle on the bottom of the dam while cyanide residue in the water, is naturally degraded through exposure to the sun. This water is then pumped to the process water pond (a surge facility) before it is required for processing.

Water from the levees is pumped directly to the process water pond. Water levee levels are strictly monitored, particularly after a minor discharge from an overflow in 2003, when heavy rainfall caused one levee to collapse, forcing water into the next levee which consequently also collapsed, resulting in flooding of the environment. Immediate remediation measures were taken, including water sampling inside and outside the concession area to determine the level of local water body contamination as a result of silting; fish caught in the flood waters were removed to the dam; all regulatory bodies were informed; and the two affected levees were reconstructed: freeboard has been increased and spillways located in competent ground.

To ensure that no flooding occurs at the suspended underground project, a care and maintenance programme has been implemented to ensure that excess water is routed to the process plant where it supplements process water supplies. A comprehensive programme is in place to prevent spillages at the tailings dam itself. The programme includes grassing of the embankment, securing the tailings discharge joints to avoid breakage, inspections, audits and regular patrols; and the establishment of an Emergency Response Management Programme.

Excess water is used to fill up the water bowsers, or tankers, which sprinkle water regularly on haulage roads to minimise dust emissions.

Should an environmental issue present, communities have recourse to the mine through the human resource department which is charged with community relations. Complaints are investigated and the necessary remedial action taken. A possible indication of the success of Bibiani’s environmental management programme is that no complaints were received in 2005. Bibiani’s environmental department has recently requested to be represented on the district assembly, a community body which also deals with issues and grievances.