Everything about Placer Deposit totally explained
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.
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 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 like
gold,
copper, and the
platinum group members will accumulate in placers, when they're 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:
Further Information
Get more info on 'Placer Deposit'.
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