In
geology, eluvium or eluvial deposits are 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 horizons, 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 soil horizon 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
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and other resistant
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
s.
Eluvial
ore deposits are those such as
tungsten and
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
placer deposits formed by settling and enriched by the winnowing or removal of lower density materials.
Diamond
Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...
s within ''yellow ground'' (weathered portions of
kimberlites) may be considered to be eluvial deposits.
Cassiterite and
columbite-tantalite deposits also occur as residual or eluvial concentrations. The
Pitinga tin deposit in
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, an eluvial deposit, is one of the largest tin mines in the world. Weathering ''
supergene'' enrichment of an
apatite rich
carbonatite in
Ontario
Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
has produced a significant eluvial
phosphate ore deposit.
See also
*
Alluvium
Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...
*
Colluvium
Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, Sheet erosion , sheetwash, slow continuous downslope creep, or a va ...
*
Diluvium
*
Lessivage
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
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Economic geology
Sedimentology
Soil science
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