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.
Cliff mine
The Cliff mined a fissure vein of native copper in Precambrian conglomerate and basalt beds. The vein was nearly vertical, dipping steeply to the east, and running north-south, nearly perpendicular to the strike of the enclosing beds. The productive part of the vein was below the Greenstone flow, which forms the cliff from which the mine took its name. The mine started by mining only high-grade ore; in 1848, the average grade mined was 26% copper. The average ore grade mined declined over time, and by 1869 was 3% copper, comparable to other copper mines of the time. Some native silver was also recovered; approximately 41,000 ounces total silver was reported recovered in the years 1846-1852 and 1858-1871.