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.

See also: list of minerals