Hard Rock and Open Pit Mines
Hard rock mining refers to various techniques used to mine ore bodies by creating underground "rooms" or stopes supported by surrounding pillars of standing rock. Terms for this include
stope and pillar
room and pillar
vertical crater retreat
sub level caving
Hard rock mining is used for mining many ore types such as gold, copper, zinc and diamonds.
There are a number of mining methods that are used to extract the mineral bearing rock from the host rock. Typically some means of support is required in order to maintain that openings that are made by mining. This can be done by pillars which are then mined following the backfilling of the initial stopes.
Coarse ore is mucked out using gravity to help move it down rock raises or shafts to waiting trains of ore cars used to move it to the surface These trains can travel through long drifts or tunnels ending in portals to the mills on the surface. Ore is also moved in skip buckets hauled up shafts and emptied into bins beneath surface headframe towers for transport to the mill. Ore is also hauled in large trucks up declines to the surface.
Open pit mining is used in shallow orebodies, often at much lower grades of mineralisation.
The El Chino mine located near Silver City, New Mexico is an open-pit copper mineOpen-pit mining refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow. 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). Where minerals occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock— underground mining methods are used to extract the valued material. Open-pit mines are typically enlarged until the mineral reserve is exhausted.
Open-pit mines that produce building materials are commonly referred to as quarries. People in some English-speaking countries are not likely to make a distinction between an open-pit mine and other types of open-cast mines, such as quarries, borrows, placers, and strip mines.
When they are no longer productive for extraction of material, open-pit 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.
A coquina quarryMaterials typically extracted from open-pit mines include:
Gravel and stone (stone refers to bedrock, while gravel is unconsolidated material, as found in glacial or fluvial deposits)
Metal ores: such as copper, iron, gold, and molybdenum