Factsheet 12 - McArthur River Mining

Fact Sheet 122007 Mine Management PlanTailings and Tailings Storage FacilityTailingsTailings are essentially the slurried waste products leftover from the production of McArthur River Mining’s(MRM’s) zinc product (bulk concentrate).Tailings Storage Facility (TSF)Waste water and solids from the MRM processing plantare taken by pipeline to the nearby tailings dam onthe west-side of the Carpentaria Highway, south ofSurprise Creek.The storage facility is divided into three cells for differentqualities of water. Cell 1 and 2 are where the tailings areinitially pumped to. The third area is a water managementdam which recycles water within the processing plant. TheTSF plays an important role in reducing water use on site. In2005, MRM recovered 87% of water through recycling.DesignUnder the open pit development, the total area takenup by the TSF will not change but it will be extendedaway from Surprise Creek. New deposits will be placedLayout of expanded Tailings Storage FacilityNovember 2006www.mcarthurriver.com.au

Fact Sheet 12 Tailings and Tailings Storage Facilityin cells furthest away from the creek. Then the cellsnearest Surprise Creek will no longer be used. They willbe rehabilitated which means emptied of water, the landgraded, capped and revegetated.MRM considered relocating the TSF as part of the openpit development. However, all alternative sites withinthe region have similar soils and therefore provide nobenefit in terms of seepage control. The current sitewas found to offer the best environmental performancebased on technical performance, seepage control andlowest long-term risks.MRM also considered a number of options for the designof the TSF but found the best is one which combines six“lines of defence” or strategies to guard against seepageand protect the environment. This strategy will be usedfor the design, operation, and ultimate closure andrehabilitation of the TSF.It aims to improve the way the tailings facility workswhile ensuring there is no uncontrolled emissions tothe environment and minimising the area disturbed forthe facility.Complies with Australian standardsThis design for the MRM TSF is in line with the standardsset by the Australian National Committee on Large Dams(ANCOLD) Guidelines (1999). That means the facilityis built to the same safety standard as all major waterstorage dams.ANCOLD has specific guidelines for Tailings Dam Design,Construction and Operation. These are regarded as thebest practise standards under Australian conditions andare recognised as the industry standard by State andTerritory Governments.Comments that the MRM TSF would not be approved inVictoria or Queensland are unfounded. The QueenslandEnvironment Protection Agency has said the designfor the MRM TSF is consistent with their guidelines.The Victorian Guidelines state the design of large TSFsshould be in line with the ANCOLD Guidelines which iswhat MRM has done.Six lines of environmental protection1. The way the tailings are deposited in the cellsSpreading the tailings in thin layers against the cell wallprovides a ‘beach’ of tailings between the water and thewall which will help block water from seeping. This alsooffers a number of benefits in the management of thetailings as it:• Supports the system of raising the embankments toincrease the tailings capacity• Limits the potential for oxidation of tailings which iswhat generates sulphates (like salt deposits).2. The way the outside wall is builtThe high embankment around the outside of the TSF ismade of compacted clay and topped with rocks whichwater will find it hard to pass through. This two metrethick, four-layered cover system is designed to be safeand stable in both wet and dry seasons. Only non-acidforming material is used for this outer surface to ensurethere are no contaminants in the water run-off.3. The continued use of geopolymer barriersIn the past two years, MRM has successfully trialled ageopolymer barrier on 2.25km of the existing TSF wall.Under this system, a glue-like polymer is injected everytwo metres around the base of the TSF wall. This forms ahard ground-level barrier that helps stop seepage outsidethe wall and will be applied to the whole perimeter.

Fact Sheet 12 Tailings and Tailings Storage Facilityand filled the dam to near capacity. On this occasion,MRM received approval from the Department of PrimaryIndustries, Fisheries and Mines to discharge clean waterfrom the tailings dam under the terms of the MRMdischarge licence. Samples that were taken daily to checkthe quality of water showed that the water leaving themine site was of drinking water quality.Closure planThe Mine Management Plan also outlines a closure andrehabilitation plan for the tailings. This is at least 25years away and so the final plan, when the time comes,will include emerging best practice and new technologyas relevant.The current plan involves:• Re-profiling the tailings surface and grading it so itpromotes surface runoff and prevents ponding• Constructing a cap across the final landform and asurface water management system to collect rainfalland release this clean water into the surroundingenvironment in a controlled way• Continuing to monitor the recovery bores andmonitoring bores to check for seepage andgroundwater levels.MRM has made a commitment to the long termmanagement of the tailings, even after the minehas closed, until such time that the monitoring andmaintenance is assessed by the Northern TerritoryGovernment to be no longer required. The aim is toensure the tailings has no lasting legacy on theenvironment or for future owners of the land.McArthur River MiningPO Box 36821 Winnellie NT 0821Phone: 1800 211 573Email: mrmprojenq@xstrata.com.auWebsite: www.mcarthurriver.com.auFIRST CLASS IN GRAPHIC DESIGN