Environment

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In preparation for mine closure in 2010, Morila mine in Mali is conducting technical studies at its tailings storage facility (TSF) and waste rock dump to establish the most efficient and cost-effective rehabilitation measures at these two sites.

The pilot study, which is being carried out by Morila’s on-site environmental team, is investigating whether mine-specific factors might have an impact on generally accepted best practice closure plans. Because operating and climatic conditions vary from operation to operation and from country to country, the trials may prove that there is no ‘one-size-fits-all’ model. For example, generally accepted best practice might specify that 300 millimetres of topsoil is needed for effective revegetation of a non-specific waste rock dump, whereas technical studies might indicate that at Morila the volume of topsoil needed could be reduced drastically, if mixed with non-acid forming waste rock. This would obviously have significant cost advantages.

A number of simulated tests are being undertaken at both the TSF and waste rock dump, both of which will eventually be rehabilitated with rock and/or soil and, in the case of the waste rock dump, revegetated with indigenous trees. Tests are being conducted at the TSF to determine the chemical characteristics of the various tailings types, and their potential to produce acidic leachate, also known as acid rock drainage. This leachate can potentially contaminate ground and surface water.

The results of the test will inform the type and amount of cover required to cap the TSF. Using two-metre high columns, the experiment simulates the effect of rainfall and in-situ water on layers of tailings materials, to analyse the best cover type, its thickness and composition, as well as what quantity will be required to prevent significant leaching.

The final cover for the waste rock dump, where non-gold-bearing ore is discarded, as well as slopes of the TSF, requires the addition of some organic matter to stimulate vegetation growth. Analysis is being conducted on what ratio of rock and soil combinations provide the best stability and minimal erosion.

Other expected outcomes from the technical studies are that restoration measures at both the TSF and waste rock dump should prove to be sustainable over a long period of time. It is expected that the amount of topsoil cover will be minimised, through the additional use of waste rock, which is in plentiful supply. This is also expected to minimise erosion which compromises slope stability. The studies will also identify the most suitable local plant species for the restoration of vegetation.

The technical studies commenced at the beginning of 2005 and are expected to continue for two years, after which they will be subject to an external independent review for the purposes of validation and verification.