The Full Wiki

Placer deposit: Wikis

Advertisements
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Did you know ...


More interesting facts on Placer deposit

Include this on your site/blog:

Encyclopedia

From Wikipedia, the free encyclopedia

Black sand concentrates

In geology, a placer deposit or placer is an accumulation of valuable minerals formed by deposition of dense mineral phases in a trap site. The name is from the Spanish word placer, meaning "alluvial sand". Types of placer deposits include alluvium, eluvium, beach placers, and paleoplacers.

Alluvial placers

Typical locations for alluvial placer deposits are on the inside bends of rivers and creeks, in natural hollows, at the break of slope on a stream, the base of an escarpment, waterfall or other barrier, within sand dunes, beach profiles or in gravel beds.

Section of Alluvial Placer Deposit at the Blue Ribbon Mine Alaska
Beach placer deposit of heavy minerals (dark) in a quartz sand (Chennai, India).

Alluvial placers are formed by the deposition of dense particles at a site where water velocity remains below that required to transport them further. To form a placer deposit, the particles sought after must show a marked density contrast with the gangue material, which is able to be transported away from the trap site. Only if the deposit is winnowed in this way can the minerals be concentrated to economic levels.

Placer materials must be both dense and resistant to weathering processes. Placer environments typically contain black sand, a conspicuous shiny black mixture of iron oxides, mostly magnetite with variable amounts of ilmenite and hematite. Valuable mineral components often occurring with black sands are monazite, rutile, zircon, chromite, wolframite, and cassiterite.

Exceptionally dense substances such as gold and the platinum group members will accumulate in placers, when they are present. Placer mining is an important source of gold, and was the main technique used in the early years of the California Gold Rush.

Substances commercially mined from placer deposits:

See also

External links

Advertisements

Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message