Mineral Deposit

an accumulation of natural mineral raw material of industrial significance. Mineral deposits of sedimentary origin occur in layers (for example, deposits of coal, salts, phosphorites, aluminum and manganese ores, and limestone) that are often intensively deformed—bent into folds and broken by faults. Mineral deposits in the crust of weathering (iron and nickel ores and other residua) may have a mantle-like, platelike, pocket, or vein form. Deposits of endogenous beds of copper, lead, zinc, tungsten, tin, and gold usually occur in veins; they may also occur in the form of lenses, pipes, stocks, and nests composed of massive ores or in the form of stock works formed by vein-impregnated ores.

Deposits of petroleum and gas are divided into sheet and massive deposits. In sheet deposits the accumulation of petroleum and gas is related to strictly defined strata—the collectors. Massive petroleum and gas deposits fill up protrusions of permeable rock, which are enclosed from above by impervious layers; they are subdivided into deposits in structural, reef, salt, and erosion protrusions.

an accumulation of mineral matter on the surface or in the earth’s interior that results from geological processes and whose quantity, quality, and conditions of bedding make it suitable for industrial use. Deposits may be gaseous (hydrocarbon fuel gases, as well as noncombustible gases, such as helium, neon, argon, and krypton), liquid (petroleum and subterranean water), or solid (precious elements, crystals, minerals, and rocks). Mineral deposits are divided into metalliferous, nonmetalliferous, fuel (caustobioliths), and hydromineral types, according to industrial use. Deposits of subterranean waters (drinking, industrial, balneological, or mineral waters, as well as waters in productive oil strata that contain bromine, iodine, boron, radium, and other elements in sufficient quantity for extraction) differ from other mineral deposits in that the reserves are replaceable. The minimum quantity of mineral and lowest grade of quality for exploitation are called the industrial conditions.

Mineral deposits may emerge at the earth’s surface (open deposits) or be buried underground (closed, or concealed, deposits). Deposits are subdivided into series according to conditions of formation (sedimentogenic, magmatogenic, and metamorphogenic), and the series in turn are broken down into groups, classes, and subclasses.

Sedimentogenic (surface and exogenous) mineral deposits were formed at the surface or in the surface zone through chemical, biochemical, and mechanical differentiation of mineral substances caused by the earth’s external energy. Three groups of mineral deposits are identified within the sedimentogenic series: (1) weathering, (2) placer, and (3) sedimentary.

Magmatogenic (deep-seated and endogenous) mineral deposits were formed in the earth’s interior through geochemical differentiation of mineral substances caused by the appearance of magma and its effect on the environment owing to sources of energy within the earth. Five basic groups are identified within this series: (1) magmatic, (2) pegmatite, (3) carbonatite, (4) skarn, and (5) hydrothermal.

Metamorphogenic mineral deposits originated in the process of regional and local metamorphism of rocks. In accordance with the accepted division of geological history, a distinction is made among mineral deposits of Archean, Proterozoic, Riphean, Paleozoic, Mesozoic, and Cenozoic age. A further distinction is made among deposits whose matter comes from subcrustal (mantle or basalt) and crustal (or granite) magma, as well as the earth’s sedimentary shell. According to place of formation, deposits are subdivided into geosynclinal (folded regions) and platform deposits. Four levels of formation of mineral deposits below the earth’s surface are known: ultraabyssal (more than 10–15 km), abyssal (from 3–5 to 10–15 km), hypabyssal (from 1.0–1.5 to 3–5 km), and near-surface (to depths of 1.0–1.5 km).