Ore District

a segment of the earth’s crust with deposits of a single ore or several genetically close ores; the deposits are associated with large tectonic structures, such as anticlinoria, synclinoria, median masses, shields, syneclises, and abyssal fractures. An ore district is part of an ore province.

Because the tectonic structures that determine the location of ore districts in folded structures are usually associated with faults and extend linearly in one direction, ore deposits are distributed within ore districts in the form of an extended ore belt. The ore belts range in length from several tens of kilometers to a few thousand kilometers and vary in width from several kilometers to a few hundred kilometers. The chief role here is played by faults, which facilitate the rising of ore melts from the earth’s interior. A distinction is made between ore belts controlled by basement faults, abyssal fractures, and ordinary faults. Basement faults do not penetrate the rocks of the upper structural layer but the traces are marked by the belts of ore deposits located in and extended along the rocks, as in the case of the Great Silver Belt of America, which stretches from Mexico to Peru and Bolivia. With abyssal fractures are associated the belt of magmatic deposits of chromites and titanomagnetites in the Urals, the chain of hydro thermal gold deposits in the Iana-Indi-girka-Kolyma Belt, and the belt of mercury deposits in the Altai-Saian District. Ordinary faults (thrust faults, normal faults, strike-slip faults) determine the position of the gold ores and complex ores of Middle Asia, the rare-metal ores of Central Kazakhstan, the copper-molybdenum ores of Armenia, and the copper-nickel ores of the Noril’sk Ore Region.

The term “ore basin” is used to designate an ore district with a continuous areal distribution of stratiform ores, such as the Krivoi Rog Iron Ore Basin.

Ore regions, ore fields, and ore zones can be distinguished within ore districts and belts. An ore region is a geologically and geographically distinct territory within which there are developed deposits of particular ore formations, that is, groups of ore deposits of similar composition formed under similar geological and physicochemical conditions. A distinction is made between ore regions, with deposits of a single ore formation, and complex regions, with deposits of several formations belonging to one or several metallogenic epochs. The name of the ore region combines a geographic designation and the name of the most important metals in the region. Examples include the Iana-Adycha Tin Ore Region, the Aldan Gold Ore Region, the Mugodzhary Copper Ore Region, the Atasu Lead-Zinc Region, and the Fergana Antimony-Mercury Region.

An ore field is the aggregate of geographically close ore deposits common in origin and uniform in geological structure. Based on geological structure, ore fields are grouped as follows: magmatic deposits in masses of ultrabasic, basic, and alkaline rocks; skarn, pegmatite, albitite, and greisen deposits in the peripheral parts of granitic masses; hydrothermal deposits in the structures of areas of minor instrusions and dikes; hydrothermal deposits in volcanogenic structures; vein-type deposits in tectonically fractured structures; metamorphogenic deposits in the structures of zones of schist formation and flow-cleavage zones; and stratiform deposits in the structures of the stratification zones of volcanogenic and sedimentary rocks.

An ore zone is a band of rocks containing accumulations of ore minerals—irregular masses, veins, systems of veinlets, and areas of disseminated ore. It usually has the shape of a plate of variable width extended in plan view in one direction and dipping down at an angle. Zones vary widely in size and are sometimes tens of kilometers in length.