In geology, eluvium or eluvial deposits are those geological deposits and soils that are derived by ''in situ'' weathering or weathering plus gravitational movement or accumulation. The process of removal of materials from geological or soil horizons is called eluviation or leaching. There is a difference in the usage of this term in geology and soil science. In soil science, eluviation is the transport of soil material from upper layers of soil to lower levels by downward percolation of water across

soil horizon A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...

s, and accumulation of this material ( illuvial deposit) in lower levels is called illuviation. In geology, the removed material is irrelevant, and the deposit (eluvial deposit) is the remaining material. Eluviation occurs when precipitation exceeds evaporation. A

formed due to eluviation is an eluvial zone or eluvial horizon. In a typical soil profile, the eluvial horizon refers to a light-colored zone located (depending on context and literature) either at the lower part of the A horizon (symbol: Ae) or within a distinct horizon (E horizon) below the A, where the process is most intense and rapid. Yet some sources consider the eluvial zone to be the A horizon plus the (distinct) E horizon, as eluviation technically occurs in both. The strict eluvial horizon (E horizon) is typically light gray, clay-depleted, contains little organic matter and has a high concentration of silt and sand particles composed of quartz and other resistant minerals. Eluvial ore deposits are those such as tungsten and gold placer deposits formed by settling and enriched by the winnowing or removal of lower density materials. Diamonds within ''yellow ground'' (weathered portions of kimberlites) may be considered to be eluvial deposits.

Cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains t ...

and

columbite-tantalite Coltan (short for columbite–tantalites and known industrially as tantalite) is a dull black metallic ore from which the elements niobium and tantalum are extracted. The niobium-dominant mineral in coltan is columbite (after niobium's original A ...

deposits also occur as residual or eluvial concentrations. The Pitinga tin deposit in Brazil, an eluvial deposit, is one of the largest tin mines in the world. Weathering ''

supergene A supergene is a chromosomal region encompassing multiple neighboring genes that are inherited together because of close genetic linkage, i.e. much less recombination than would normally be expected. This mode of inheritance can be due to genomic ...

'' enrichment of an

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

rich carbonatite in Ontario has produced a significant eluvial phosphate ore deposit.

References

* Gupta, Chiranjib Kumar (2002) ''Chemical Metallurgy: Principles and Practice'', Wiley, * Cronan, David Spencer (1999) ''Handbook of Marine Mineral Deposits'', CRC Press, * Swiecki, Rafal (2006
''Eluvial Placers''
Accessed 18 April 2006 * Van Hees, Edmond H., (2002) ''Supergene Phosphate Enrichment in Carbonatite-Derived Eluvial Sediments: Agrium Phosphate Mine, Kapuskasing, Ontario, Canada'', The Geological Society of America (GSA

Accessed 18 April 2006 {{Authority control Economic geology Sedimentology Soil science de:Eluvium

See also

References