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 the 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. The closure program is believed to be among the world’s finest examples of environmentally sensitive mine closure and rehabilitation.
Following completion of the active closure phase from April 2014- February 2018, Lisheen entered the passive mine closure phase due to conclude in December 2019. This will be followed by planned aftercare to commence phase from January 2020- December 2050.
The Mine Closure Plan forms part of the Closure Rehabilitation and Aftercare
Management Plan (CRAMP), was developed over many years – beginning with the original closure plan approved by the relevant Irish authorities. In the development of the plans, Lisheen and Vedanta used both their in-house expertise and international experts on mining and mine closure from around the world.
Lisheen is responsible for:
- Ensuring that the underground workings cannot collapse leading to surface subsidence Removing all surface and underground plant and equipment
- Allowing the mine workings to refill with clean water
- Blocking and sealing all access to the underground workings
- Fully engineered covering of the tailings deposition facility to provide a multiple of possible after uses from animal grazing to solar power or energy crops
- Creating a space that will be attractive to other industries
- Supporting Lisheen staff during the closure, from upskilling and training grants to redeployment at other Vedanta operations
- Underground support
Some important points
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.
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 sulfide ore remnants has occurred. These salts are sinking to the footwall, creating an overlying layer of pure water – a chemocline — with metal sulfates 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 liters of potable water for the local communities.
Tailings deposition restoration
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 stabilized 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.
Lisheen’s employees who no longer have worked 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.
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 the surface before the rise in underground water levels rendered this impossible. All surface equipment and underground have been sold, with a large proportion being exported to mines abroad.
Closing and sealing access to the old workings
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 concrete plugs reinforced with steel rebar. The surfaces left behind have been leveled 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 were placed along 130m of the decline. This now provides a robust and geotechnically competent plug.
Alternative industrial use
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 bio-economy campus powered by wind turbines that dot the neighboring 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 bio-economy. 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.
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.