Lisheen Mine Tailings Management Facility – progressive reclamation project

Abstract

The Lisheen Mine is an underground lead and zinc mine located in North Tipperary, Ireland. Construction commenced in 1997 and the mine has been in production since 1999. The mine is fully owned by Vedanta Resources plc. and is currently expected to close in late 2013 or early 2014. The Lisheen Tailings Management Facility (TMF) is located in an area of peat bog; it is lined with a plastic liner and has an internal area of around 64 hectares. Upon closure the facility will contain over 9 million tonnes of tailings. Lisheen Mine tailings have a significant net acid generating potential. The management of this risk at Lisheen Mine has been the subject of considerable geochemical and geophysical test work and this has supported the development of a practical strategy for residual liability management through progressive rehabilitation of the TMF. In January 2008, Lisheen commenced a progressive rehabilitation programme on the Lisheen Mine TMF. This involves depositing tailings using spigot discharge pipes placed on the dam wall, to progressively form beaches. These beaches are then capped by firstly placing a geotextile directly on the tailings, followed by a 700 mm deep layer of limestone rock and then a 400 mm deep layer of soil forming material. This soil forming material is produced by mixing peat with glacial till in a ratio of 1:1. The peat is sourced from the initial construction of the TMF, where peat was excavated out from under the wall footprint and stockpiled. The glacial till was sourced from the Lisheen Wind Farm; an 18 turbine 36MW project completed in 2009. The cap is then seeded with native grassland, herb and wildflower species. To date approximately 9 hectares of the facility has been rehabilitated and extensive monitoring data is being collected. In July 2010, Lisheen initiated a livestock trial programme by introducing ten cattle onto the rehabilitated area. This trial is ongoing. Lisheen intends to continue to rehabilitate the TMF over the coming years in the manner outlined in this paper. The global objective of the project is to rehabilitate the facility such that it is secure, sustainable and can be used for the widest possible range of potential after uses.