Authors: Lagunas, H; Weeks, B; Bocking, K; Salfate, E

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Lagunas, H, Weeks, B, Bocking, K & Salfate, E 2008, 'Mine Closure Planning in the High Andes: Collahuasi — A Case Study', in AB Fourie, M Tibbett, I Weiersbye & P Dye (eds), Mine Closure 2008: Proceedings of the Third International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 277-284,

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The Collahuasi Mine, operated by the Companía Minera Doña Inés de Collahuasi (CMDIC), presents an unusual case study illustrating closure planning for a mine located in two distinct – and exceptional – environments. The mine site is located in the Altiplano of Chile, at an elevation of over 4000 m above sea level (m.a.s.l.), within closed watersheds that drain to Andean salars. Annually, the Collahuasi Project produces in the order of 450,000 tons of copper concentrate and 70,000 tons of copper cathodes, as well as molybdenum concentrate. This high Andean mine site is joined to a coastal port and processing facility (that includes a molybdenum plant) by means of a 200 km pipeline. The port facility is located in one of the driest regions in the world, where annual average precipitation is not measurable. These extreme environments present unusual conditions for closure planning. Despite being literally decades away from closure, CMDIC has incorporated closure planning into their operations from an early date. Thanks to the incorporation of closure planning in the design and development stages of the mine, several important areas, such as the tailings dam and the waste rock dump slopes, have been designed (and are being constructed) to meet closure criteria. This has helped to simplify the closure plan and reduce the projected risks at closure. In 2003, in the absence of specific closure plan regulations in Chile, the CMDIC undertook the development of a comprehensive closure plan for the site. This closure plan has been subsequently revised, with the most recent plan having been developed in anticipation of new Chilean regulations that will require all operating mine sites to have closure plans approved by the mining ministry in 2009. This most recent plan for the mine was developed using a risk assessment methodology, to focus closure efforts on the areas which present the greatest potential risk after closure. This paper presents an overview of the development of the closure plan and some of the more interesting technical implications of it, such as evaluating the risks of contaminant transport in areas of virtually no rain, and addressing the closure needs of a tailings impoundment with an area of over 2300 ha located at the border between two salar regions. The closure plan also takes into account plans for the closure of dozens of small abandoned mine sites located around the property, a legacy of a mining history on the site that dates back to 1880.

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