Open-pit mining, also known as opencast mining and open-cut mining, refers to a method of extracting rock or minerals from the earth by their removal from an open pit or barrow.
The term is used to differentiate this form of mining from extractive methods that require tunneling into the earth. Open-pit mines are used when deposits of commercially useful minerals or rock are found near the surface; that is, where the overburden (surface material covering the valuable deposit) is relatively thin or the material of interest is structurally unsuitable for tunneling (as would be the case for sand, cinder, and gravel). For minerals that occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock— underground mining methods extract the valued material.
Open-pit mines that produce building materials are commonly referred to as quarries. People in some English-speaking countries are unlikely to make a distinction between an open-pit mine and other types of open-cast mines, such as quarries, barrows, placers, and strip mines.
Open-pit mines are typically enlarged until either the mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to landfills for disposal of solid wastes. However, some form of water control is usually required to keep the mine pit from becoming a lake.
Gilbert Mine, St. Louis County, Mesabi Range, MN - 1909
Biwabik Mine, Biwabik, MN - 1895
Hull-Rust-Mahoning Mine, Hibbing, St. Louis County
Portsmouth Mine, Crosby, Cuyuna Range, Crow Wing County
Hull-Rust-Mahoning Mine, Hibbing, St. Louis County 1930