Economic deposits of minerals (ore deposits) in the Earth's crust are commonly formed by the transport of dissolved ore-forming materials in fluids (hydrothermal fluids or magmas), with ore deposition occurring at sites of fluid cooling or chemical change. Because of this dependence on fluid mobility, ore deposits are commonly located in areas of relatively high permeability, where fluid flow has been focused. Such zones may be formed by high-permeability sedimentary or volcanic horizons or layers (such as conglomerates, sandstones, or vesicular lavas) or by faulting (that is, fracturing) of otherwise impermeable rocks.

Major fault zones and permeable stratigraphic horizons are large-scale crustal features that can be recognized over wide areas, and may even be extrapolated beneath areas where younger geological materials have covered their traces. This geologic evidence provides a powerful tool for mineral exploration, particularly in areas of poor exposure or in covered terrains. Because much of the world's easily accessible land area has now been explored, and easily identified (that is, exposed) ore deposits have already been discovered, modern mineral explorers seek to locate previously hidden deposits. Extrapolation of regional-scale prospective zones beneath cover is one method for selecting early exploration targets.