Mining activity at the Lisheen Mine in Ireland was concluded in November 2015, with milling stopping in December 2015 after 17 years of operation.
Focusing on physical closure of the mine and aftercare of the site, a best practice mine closure plan has been implemented to fully address regulatory authority permit requirements.
The cessation of mining at Lisheen was not the end of the story as far as VZI is concerned. Lisheen is now approaching the end of the ‘active closure’ phase of the mine closure plan. The closure programme is believed to be among the world’s finest examples of environmentally sensitive mine closure and rehabilitation.
Following completion of the active closure; Lisheen will enter a period of passive validation – during which time the effectiveness of the closure programme will be demonstrated by monitoring and assessment. Lisheen has also provided an aftercare programme of monitoring and maintenance of the site as part of the closure plan. This will ensure the environmental conditions will remain stable into the future.
Planning for closure and the associated preparatory work has been underway for a number of years. Once mining ended, the team embarked on a multi-year programme to restore the mine site to its pre-mining state.
Lisheen is responsible for:
The mine back-filled the worked-out area, and then compacted the fill, so that the workings and their hanging walls remain supported. This has been verified by independent, external experts and the mine, who have also signed off on allowing the complete re-watering of the workings.
Ground level measurements continue to be taken from surface monitoring points and these data confirm that the ground above and around the mine workings is now fully stable with no movement. The frequency of monitoring will now be reduced but will remain during the passive validation period.
All underground equipment has been removed along with potentially hazardous oils and other products. Removal of the underground pumps was carefully managed so that the majority of pumping equipment was drawn to surface before the rise in underground water levels rendered this impossible. All surface equipment and underground has been sold, with a large proportion being exported to mines abroad.
The re-watering or controlled flooding of the underground workings is now fully complete and regional groundwater is at the pre-mining baseline elevation. Re-watering will ensure that wells, previously impacted by the mine now have a supply of water restored. The quality of this water has also been demonstrated to be at baseline conditions and suitable for consumption.
Groundwater monitoring around the area of the orebodies has demonstrated that the natural segregation of salts from the interaction of saline water with sulphide ore remnants has occurred. These salts are sinking to the footwall, creating an overlying layer of pure water – a chemocline -- with metal sulphates precipitating out of the water body as anoxic and anaerobic conditions become established. The group water scheme established by the Lisheen Mine is amongst the best in the country and will continue to provide close to 2 million litres of potable water for the local communities.
Access to Lisheen’s underground workings has been through 12 vertical surface shafts as well as through the mine’s main portal and decline. The shafts have been filled by loading boulders into them, topped by solid concreate plugs reinforced with steel rebar. The surfaces left behind have been levelled and are covered with soil and planted with grass.
Closing and sealing the main portal and decline was more complex. It was achieved by building a barrier across the decline 20 meters below the surface, above which rock and concrete was placed along 130m of the decline. This now provides a robust and geotechnically competent plug.
Lisheen’s tailings deposition facility has been carefully designed and managed since the mine’s inception in anticipation of the eventual need to restore its site to agricultural use. This is now complete with the site fully stabilised and dried. Rehabilitation was started by covering the entire surface with a geotextile material on top of which was laid a 700mm layer of limestone, itself covered by a 300m layer of soil.
This is planted with grass which will provide safe and healthy grazing for cattle. The 1,000mm limestone and soil cap ensures that the surface grass does not penetrate to the underlying tailings residues while the incorporation of an engineered wetland into the surface ensures that no deleterious run-off can occur.
While surface and underground rehabilitation has been in progress, the company has actively collaborated with local authorities and business development groups in finding possible users for a site that is well served by power, water and waste disposal infrastructure. Our vision is of a bioeconomy campus powered by the wind turbines that dot the neighbouring landscape and situated in an area of natural beauty.
Lisheen is extremely pleased with the progress that has been made in this regard. A number of companies are advanced in the plans to develop their business on the Lisheen site and this saw further investment in late 2017 when €4.6million in government aid was secured by the Irish Bioeconomy Foundation to convert the Lisheen administration building into a pilot plant for the bioeconomy. This will be a first for Ireland and will be a strategically important development for Ireland’s burgeoning bio-economy.
While there are some limited examples worldwide where mine sites have been repurposed for alternative use after mining has ceased, the development of a campus for the research and production of biochemicals will be a first and will be a flagship for the mining industry to be able to demonstrate the sustainability of mining and how value can be derived even after the mineral resource has been exhausted.
Lisheen’s employees who no longer have work at the closed mine have been found and offered positions at the Vedanta group’s other operations around the world. As a multi-national mining group VZI needs people with mining and technical skills across its global operations. The Lisheen team has established a new company Lisheen Technical and Mining Services (LTMS) to provide the group, and the industry as a whole, with its mining and technical consultancy needs.
Detailed cross section of the engineered closure design for the vent shafts. The diagram clearly depicts the different layering of materials (rock and concrete) used to seal the vent shafts including the top concrete lintel keyed into the raised bore foundation.