Translations of Encyclopedia about Geology

Ore Deposits

Places containing a sufficient amount of minerals, which may be used to obtain metals, are called ore deposits, aand minerals containing metals are called ore minerals. They are chemical compounds of metal elements combined with sulphur or oxygen. Ore in pure form is found very seldom, especially in larger pieces, they are combined generally with rock minerals, which are also important for us. Some precious or heavy metals, for example gold, occur naturally in the form of elements.

A valuable raw material is obtained by separating the ore from the host rock. A deposit is economically viable only if a certain element occurs in a substantially higher concentration than in the average rock of the earth's crust.

Deposits are formed by various geological processes. There are sedimentary, igneous, aand hydrothermal deposits.

Sedimentary deposits are among the most important raw material resources on earth. Through chemical aand physical action during the sedimentation process, many economically important minerals were separated. The most important factor in this case is the dissolving property of water. An example of this process are the silica saands. The water currents aand waves change saands to such a degree, that only pure quartz is left behind. Quartz is an important raw material in the glass industry aand for the telecommunications technology (fibre optics).

Copper, iron, aand other metals are also important sedimentary ore deposits. The most important ores are found in the Precambrian sedimentary rock. There are large deposits of this type in Brazil, India, Australia, aand North America.

Ore deposits with a high content of gold or other heavy metals, for example titanium minerals, are called placer deposits.

A well-known method of obtaining gold is the panning. By swirling a pan filled with fluvial deposits, one first separates the lighter minerals, because the heavy gold settles on the bottom of the pan.

Diamond, one of the most valuable minerals, comes to the earth's surface through thin, long tubes. Diamonds form in the depth of the upper earth's mantle, because only there the pressures are such as to allow the formation of this mineral.

Igneous deposits often occur in layers. They form, when minerals crystallise from the molten magma, sink, aand are enriched on the bottom of the igneous chamber. In southern Africa, important deposits of platinum aand chromium were find in this type of deposits.

Hydrothermal deposits form thanks to the action of hot solutions during magma melting processes, or in the hot underground water.

Minerals are separated by the hot liquids from the rock aand when they are transported to cooler rocks, they settle in the cracks aand cavities. This is how iron sulphides, zinc, aand copper form.

If the hydrothermal solutions reach the earth's surface, it gives rise to hot springs aand geysers containing mercury aand zinc. Large hydrothermal deposits are found for example in the Mississippi river basin in Kansas aand Oklahoma.

On the boundaries of colliding plates aand in subduction zones, we find other deposits, of both the hydrothermal aand igneous origin. This is an indication that there must be a link between the movement of the tectonic plates aand the formation of the deposits.

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