Glossary

Ore is a naturally occurring rock, mineral deposit, sediment, or other material that contains enough of a valuable substance to make extraction practical and economically worthwhile. The valuable substance is usually a metal, such as iron, copper, aluminum, nickel, lead, zinc, gold, or silver, but some ores are mined for nonmetallic materials as well.

An ore normally contains both the useful mineral and unwanted material called gangue. Gangue may include rock, clay, sand, silica, and other minerals that have little or no value in that particular operation. After mining, the ore is commonly crushed, ground, sorted, washed, or otherwise concentrated to separate as much of the valuable mineral as possible from the gangue.

A material is not considered an ore simply because it contains a metal. The concentration must be high enough, and the deposit must be accessible enough, for the valuable material to be recovered at an acceptable cost. Changes in metal prices, mining technology, energy costs, environmental requirements, and transportation expenses can therefore determine whether a mineral deposit qualifies as an ore. A deposit that is uneconomical today could become a useful ore in the future.

Different metals occur in different ore minerals. Iron is commonly obtained from hematite and magnetite, aluminum from bauxite, copper from minerals such as chalcopyrite, and lead from galena. The ore may contain the metal as an oxide, sulfide, carbonate, silicate, or another chemical compound rather than as pure metal.

Once concentrated, an ore may be processed by methods such as smelting, roasting, calcination, chemical leaching, or electrolysis. The exact process depends on the type of mineral, the metal being recovered, and the impurities present.

Ore should not be confused with a mineral. A mineral is a naturally occurring substance with a particular chemical composition and crystal structure. Ore is an economic term for material that can be mined and processed to recover something valuable. In practical terms, ore is the raw metal-bearing material taken from the ground and processed to obtain a useful substance.