An
alluvial
deposit
is
an
accumulation
of
alluvium
(sediment),
sometimes
containing
valuable
ore
and
gemstones,
or
simply
consisting
of
gravel
or
clay,
in
the
bed
or
former
bed
of
a
river.
Valuable
materials
such
as
gold
may
be
extracted
using
techniques
of
placer
mining.
Gems
historically
were
found
in
the
gravels
of
India
particularly
diamonds
and
continue
to
be
mined
from
alluvium
in
Myanmar
and
Sri
Lanka.
Glaciers
may
also
deposit
alluvium
known
as
till.