Reactions at North Overburden Emplacement Facility (NOEF)

Reactions at North Overburden Emplacement Facility (NOEF) August 2014 Overburden is the waste material surrounding the zinc-‐‑lead ore mined from the open pit. It includes some topsoil, clay and a variety of non-‐‑commercial rock types. It is not subject to any chemical processes but needs to be removed to allow access to the ore. At MRM, overburden is taken to an emplacement facility (OEF), also known as the waste rock dump. Over time, the dump is shaped, covered with clay and finally rehabilitated. Emissions from the dump A small proportion of the overburden being generated from the pit is reactive material which has the potential to spontaneously combust when mined and exposed to air and water. This is a natural process. Every mine is different but it is not unusual to find reactive material. For MRM, it depends on where we are mining in the pit. The result of the reaction is the release of smoke and sulphur dioxide from parts of the OEF. The smoke is highly visible, particularly in the mornings. Sulphur dioxide can pose health risks to people in close proximity to it if in high concentrations over extended periods of time. Environmental monitoring Emissions into the air from the OEF impact on a relatively small area on and adjacent to the mine site depending on the wind. Air quality monitoring stations have been established throughout the mine site, at the McArthur River Airport, along the Carpentaria Highway and at properties further away from the mine. The revised method of layering overburden has virtually stopped emissions in new sections of the North OEF. www.mcarthurrivermine.com.au | [email protected] | 1800 211 573 | PO Box 3621 Winnellie NT 0821 compacting the slope and then re-‐‑
covering the overburden. While this process initially causes an increase in the smoke, once work is complete there is a visible difference in the situation. There has been a reduction in the smoke coming from the NOEF. Work continues on the older areas to identify and treat all combustible materials. We are working with the appropriate government authorities to address the cause of emissions and manage the situation. Smoke and emissions are easing in older areas of the dump as action is taken. All our monitoring shows there is no risk to the health of the community in Borroloola or at publicly accessible points such as the MRM Airport. Water run-‐‑off from the NOEF is generally captured on-‐‑site. Water quality monitoring at our compliance point downstream shows no evidence of metals. Treatment of new waste material For new material being deposited at the NOEF, we have developed a new dumping method which involves lowering the height of benches, reducing the grade of the slope and using bulldozers to compact materials. In areas where this new process has been used we have observed no combustion of materials and we are confident this will be a long-‐‑term solution to the issue. For more information contact: Chrissy Joll Senior Community Relations Adviser McArthur River Mine Phone: 08 8975 8216 Protection for employees In close proximity to the waste rock dump on site, there have at times been elevated levels of sulphur dioxide detected. To ensure the safety of our employees and others on site, those working in affected areas are required to carry personal monitors to notify them of their level of exposure to sulphur dioxide. Guidelines for when it is safe to work, when a respirator is required and when you need to move to a safe location are set by our procedures. Staff are supported to manage their own safety by following these guidelines and contacting their manager if they have any questions. Fixing the problem A new method of layering materials at the waste rock dump is also easing the emissions from the NOEF. The reaction is occurring on older parts of the NOEF, and is being addressed by uncovering the overburden, allowing it to cool, reshaping and The older method of depositing overburden left much steeper slopes and some material was more prone to combustion. www.mcarthurrivermine.com.au | [email protected] | 1800 211 573 | PO Box 3621 Winnellie NT 0821

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