Mining activity at the Lisheen Mine in Ireland was concluded in November 2015, with milling ceasing 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, as the mine is now in an ‘active closure’ phase. The closure programme is among the world’s finest examples of environmentally sensitive mine closure and rehabilitation.
Planning for closure and the associated preparatory work have been in place for some years. With the end to mining have come the final stages of the multi-year programme of restoring the mine-site to its pre-mining state:
The mine back-filled 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.
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 progressing better than expected and we are ahead of schedule for ground-water recovery in the locality. Re-watering will mean that wells that were previously impacted by the mine will return and be able to provide potable water. Already in progress is the natural segregation of salts from the interaction of saline water with sulphide ore remnants. 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 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 of various sizes into them, topped by solid concreate plugs reinforced with steel rebar. The surfaces left behind are perfectly level and covered with soil and planted with grass. Closing and sealing the main portal and decline was more complex, but was done by building a barrier across the decline 20 meters below surface and then, above this barricade rock and concrete was placed to a length of over a distance of 130 metres along the decline, to provide a robust, 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 in progress with the site fully stabilised and dried. Rehabilitation was started by covering the entire surface with a geotextile material on top of which is 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 the local authorities in finding possible users for a site that is well served by power, water and waste disposal infrastructure. Our vision is of a bio-economy campus powered by the wind turbines that dot the neighbouring landscape and situated in an area of natural beauty.
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 to provide the group with its mining and technical consultancy needs as mining contracting services.
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.