Ingeology,eluvium oreluvial deposits are geological deposits andsoils that are derived byin situweathering or weathering plus gravitational movement or accumulation.
The process of removal of materials from geological or soil horizons is calledeluviation orleaching. There is a difference in the usage of this term in geology andsoil science. In soil science, eluviation is the transport of soil material from upper layers of soil to lower levels by downwardpercolation of water acrosssoil horizons, and accumulation of this material (illuvial deposit) in lower levels is calledilluviation.[1][2] 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 aneluvial zone oreluvial 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 ofsilt andsand particles composed ofquartz and other resistantminerals.
Eluvialore deposits are those such astungsten andgoldplacer deposits formed by settling and enriched by the winnowing or removal of lower density materials.Diamonds withinyellow ground (weathered portions ofkimberlites) may be considered to be eluvial deposits.Cassiterite andcolumbite-tantalite deposits also occur as residual or eluvial concentrations. ThePitinga tin deposit inBrazil, an eluvial deposit, is one of the largest tin mines in the world. Weatheringsupergene enrichment of anapatite richcarbonatite inOntario has produced a significant eluvialphosphate ore deposit.
