Ore

Ore is a type of rock or sediment that holds enough valuable minerals—often metals—to make mining and processing profitable. Its worth depends on the grade, or concentration, of the desired material, which must be high enough to offset the costs of extraction. Ores are dug from the earth and then refined, usually by smelting, to recover the metals or minerals inside. The word itself comes from Anglo-Saxon, meaning "lump of metal."

Most ores are not pure; they contain a mix of valuable minerals and worthless rock called gangue. The gangue is separated from the valuable ore through processes like froth flotation, gravity separation, or magnetic methods—collectively known as mineral processing or ore dressing. First, the ore is freed from the gangue (liberation), then the desired minerals are concentrated. After processing, the leftover gangue becomes tailings, which are useless and can be hazardous, especially when produced in large amounts from low-grade deposits.

An ore deposit is a concentrated accumulation of minerals that is economically worth mining, as opposed to a mere mineral resource. These deposits are often named after their location, a discoverer, a historical figure, a place, a mythological name, or even a company's code name. They form through various geological processes—called ore genesis—and are classified by deposit type.

Magmatic deposits come directly from magma. Pegmatites are coarse-grained igneous rocks that crystallize slowly deep underground, yielding large crystals and industrial minerals like quartz and feldspar. Carbonatites, made mostly of carbonate minerals, form from mantle magmas at continental rifts and are rich in light rare earth elements. Magmatic sulfide deposits arise when mantle melts pick up sulfur from the crust, causing sulfide minerals to separate out. These include nickel-copper deposits (found in komatiites, anorthosite complexes, and flood basalts, including the unique Sudbury Nickel Basin from an asteroid impact) and platinum group element deposits from large mafic intrusions. Stratiform chromites, linked to these sulfides, form layered deposits of chromite (the only chromium ore), often in continental cratons like the Bushveld Complex. Podiform chromitites occur in ultramafic oceanic rocks from complex magma mixing. Kimberlites, originating 150 km deep in the mantle, are the primary source of diamonds.

Metamorphic deposits result from metamorphism. Skarns are silicate rocks formed when carbonates like limestone recrystallize through contact or regional metamorphism, or by fluid-related metasomatism; they are diverse and classified by dominant elements like calcium or iron. Greisens are quartz-mica deposits altered from granite by intruding magmas, providing tin and tungsten ores such as cassiterite and wolframite.

Porphyry copper deposits are the main source of copper ore, forming along convergent plate boundaries.