Mining is a temporary activity as the resources being extracted are finite. The lifespan of a mine can span anywhere from a couple of years to decades depending on the size and quality of the deposit. A mine will close once all of the resources are exhausted or if the operation is no longer profitable. In modern times closure of a mine must be planned before the mine is even opened. This plan must be in place to show that the site will not pose a threat to the environment in the future.
Mine closure is a long process. Initially the mine will cease operation and only a skeleton crew will remain on the site to shut down machinery permanently. The mine is then decommissioned, the equipment is taken apart, cleaned and sold, pipelines are drained, on-site buildings are repurposed or demolished and waste materials are disposed of.
The process of remediation is then started. Remediation is the process of returning the land to a natural state or to a state in which it can be used for a different purpose. This remediation process ensures the structures are made stable and watercourses have an acceptable level of water quality so as not to pollute lakes, rivers or other water sources. During this process any hazardous material is disposed of and the land is reshaped to a stable structure. Topsoil is replaced and grasses and trees are planted.
Lisheen Mine in Co. Tipperary has begun its remediation programme.
Land above the mine is still used for peat extraction and generating wind energy for the nearby residents.
Even after all of these steps are completed the mine must still be monitored. Environmental concerns such as water quality are closely monitored and ongoing maintenance work is carried out.
Spoil heaps also pose a threat to the environment, these are the piles of waste rock excavated during mining. They often contain elevated levels of metals that can be washed into water sources. This can pose a huge threat to water quality and have knock on health effects to the plants, animals and people who rely on these water sources.
A key example of issues relating to mine closure in Ireland is Avoca in county Wicklow. From the 1720's to the 1980's the Avoca mine was active, the principal mineral being mined was copper but silver, iron and smaller quantities of gold were also extracted. The mine was closed in 1982 but the mine is still having serious effects on the environment. The mine itself, still having some open pits, along with large spoil heaps pose a threat to water quality of the surrounding area. Pollution of the Avoca River by mine water from the abandoned mines is a long-recognised problem. The river is considered by the EPA to be the most metal polluted river in Ireland.
The Geological Survey has carried out studies working to identify any hazards at the former mine site and monitoring conditions to ensure there is no undetected hazards.