Suction Dredging for Gold

There have been many advances in modern gold mining methods over the past 150 years, and today the suction dredge is one of the most efficient and effective gold recovery tools used by the modern day gold prospector. A suction dredge essentially works like an underwater vacuum cleaner. It sucks up the streambed materials using a suction hose and processes it through a recovery system floating on the surface of the water. The recovery system separates and retains the heavier materials (gold, black sands. etc.) and discharges the lighter materials (rocks, sand, and gravels) out the back of the sluice.

Suction dredges are rated into different sizes based on the inside diameter of the suction hose, but the end of the hose should have a suction tip that has a slightly reduced diameter to help prevent rocks and other material from clogs in the main hose.

Different states will have different regulations and restrictions on how big a gold dredge can be. Common sizes include 2", 2.5", 3", 4", 5", 6" and larger, but be aware that the manufacturer generally measures the diameter of the main suction hose. The diameter of the suction tip (or nozzle) will be the limiting factor on how much material you can process, thus most dredging restrictions are based on the tip diameter, not the main hose diameter.

Generally speaking, the more material you can process the better, so it is a good idea to use the largest sized dredge you can legally use in a waterway to recover the most gold.



A dredges basic setup involves a sluice box mounted between two pontoons, with a motor and pump system and suction hose. The pump creates pressure in the suction hose to vacuum up the gravels from the streambed. This material is then pulled up the suction hose to the surface where it is processed through a sluice box. The gravels are run over a series of riffles, lighter material is discharged out the back and the heavier materials (concentrates) are retained.

At the end of the day, the miner washes out the concentrates from the sluices riffles and carpeting for further processing. At this point it has been processed down to the highest grade material, and all that needs done is to pan out the concentrates to recover the gold.

Although it may not be necessary in low water conditions, dredgers almost always use a snorkel and wetsuit so they can dive underwater and work uninterrupted. Many gold dredgers use a hookah air system, which supplies oxygen from the surface via an air compressor. This allows the modern-day prospector to access deep water areas in a river that may have been inaccessible to the early day miners who didn't have this technology, thus a higher potential for good gold recovery.

Gold dredges are a bigger investment than many other types of mining equipment. A new gold dredge will generally cost between $2,000 and $6000 depending on the size. However, the initial investment may very well pay off for a hard working gold prospector who works hard and finds the gold.

(photos courtesy of Gold Dredge Builders in Riggins, Idaho)

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