What is an ore in geology ?

Ore : definition

The term ore does not benefit from a unanimous definition, because it carries a meaning more economic than geological. In general, it designates a group of rocks containing one or more elements (metals or useful substances) in a sufficiently large proportion to allow exploitation under economically profitable conditions.

This definition therefore encompasses both the mineral carrying the useful element (ore in the strict sense, such as galena PbS, lead ore), and the formation or geological structure containing the recoverable mineral (ore in the "broad" sense or "mining"): a sandstone impregnated with hematite is thus an iron ore, a vein of quartz and galena is a lead ore, although the proportion of strict ore, galena, is a few percent. In the case of gold, the ore is often a vein of sulphide and gold quartz, in which the ore in the strict sense, native gold, is only a few grams per tonne.

The term ore is restricted to essentially metallic elements, industrial minerals, and includes energetic substances and building materials. Sphalerite (ZnS) is for example a zinc ore, cinnabar (HgS) is an ore of mercury (liquid), and fluorite (CaF2) the main mineral of a gaseous element, fluorine, while a shale rich in andalusite is an ore of andalusite.

The ore concept evolves in time and place according to economic conditions and with existing technology. Bauxite, for example, did not become an aluminum ore until the 19th century, when technological advances made it possible to extract aluminum from it on an industrial scale.