Open-pit mining
After mining finishes, the mine area may undergo land rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels. Instead of returning the land to its former natural state, it may also be reused, converting it into recreational parks or even residential/mixed communities.
Slate industry in Wales
In Blaenau Ffestiniog, the Llechwedd Slate Caverns have been converted into a visitor attraction. Visitors can travel on the Miners' Tramway or descend into the Deep Mine, via a funicular railway which uses an old incline, to explore this former slate mine and learn how slate was extracted and processed and about the lives of the miners. The Deep Mine, opened in 1979, is accessed by Britain's steepest passenger railway, with a gradient of 1:1.8 or 30°. In the chambers, formed by slate extraction, sound and light is used to tell the story of the mine and mining. The Braichgoch slate mines at Corris have been converted into a tourist attraction named "King Arthur's Labyrinth" where visitors are taken underground by boat along a subterranean river. They then walk through the caverns to see audiovisual presentations of the Arthurian legends and stories from the Mabinogion and the tales of Taliesin. The Llwyngwern slate quarry near Machynlleth is now the site of the Centre for Alternative Technology. A number of the railways which carried the slates to the ports have been restored as tourist attractions, for example the Ffestiniog Railway and the Talyllyn Railway.