Sedimentary Deposits

mineral deposits formed during the accumulation of sediment on the bottom of rivers and other bodies of water. According to their place of formation they are divided into river, swamp, lake, sea, and ocean deposits. Among ocean deposits a distinction is made between platform and geo-synclinal deposits. Depending on the type of sediment accumulation, sedimentary deposits may be mechanical, chemical, biochemical, or volcanic-sedimentary.

The physicochemical and geological conditions under which sedimentary deposits are formed are related to the general process of the formation of sedimentary rocks. Sedimentary deposits are conformable with respect to the sedimentary rocks enclosing them. They usually occupy a strictly defined stratigraphic position and occur in the form of layers or flat lenses. Sometimes, as a result of metamorphism and tectonic movements, they become deformed and acquire more complex contours. Some layers may stretch for dozens of kilometers and reach thicknesses of 500 m (the Solikamsk salts). The mineral composition of sedimentary deposits is determined by three groups of minerals: (1) weathering-resistant detrital minerals carried from the continent (quartz, rutile, and sometimes feldspar, pyroxene, amphibole, and mica), (2) products of chemical weathering (kaolinite, mont-morillonite, hydromica, opal, hydroxides of Fe and Mn), and (3) new sedimentary formations (carbonates, salts, phosphates, ore minerals, siliceous products, hydrocarbons).

Sedimentary deposits are extremely important industrially. They include all deposits of combustible minerals (petroleum, gas, coal, and combustible shales), some ores of iron, manganese, and aluminum, and several nonferrous and rare metals (U, Cu, V). Among sedimentary deposits are mineral salts, phosphorites, and large deposits of such building materials as gravel, sand, clay, slate, limestone, chalk, dolomite, marl, gypsum, jasper, and tripoli.