Dredge mining is the mining of sediment deposited from flowing water, such as gravel, sand, and rock, to collect valuable materials, such as gold. Generally, the sediment is suctioned up from the bottom of a water body or buckets are used to scoop up the sediment. Dredge mining is the technique that is often used by commercial and recreational miners to collect raw gold. When dredge mining for gold, the dredge is used to dig, sort the materials, collect the gold, and discharge the unwanted sediment.
Most recreational gold mining is done through suction dredge mining, also called modern dredging. The suction dredge is easy to operate by one or two individuals, making it quite popular in areas where raw gold is located. Generally, the suction dredge vacuums up sediment through a hose that is located on the river or creek bottom. After the sediment is suctioned to the surface of the dredge, it is processed and sorted through a sluice. The sluice is used to remove any valuable materials, while the waste sediment is typically discharged from the dredge.
Although suction dredge mining is easy to use and popular, there are several other forms of dredge mining that are also used, particularly by commercial miners. For example, flume sluice dredging uses a bucket to dig up sediment and process it through a sluice in shallow waters. A screen and flume dredge is used to work with larger rocks, separating sediment from the larger materials using a screen that revolves. A table stacker dredge uses a series of buckets to dig up sediment and separate it from valuable materials through sluices.
Although dredge mining has been used for centuries, there are some environmental concerns related to the technique. For example, there are concerns that it may alter a river’s shape and muddy its waters by unsettling the silt. In addition, some researchers claim that dredge mining may release mercury into the river when the sediment is disturbed. The fear is that fish, such as salmon, may be harmed by the mercury.
In some areas, such as California, there have been limits and judicial moratoriums placed on dredging. The miners have responded to these limits by claiming that they can help river ecology by preventing over-sedimentation. They also claim that by removing sediment from the rivers, the temperature of the river water will be cooler and better for river life.