Gold dredges provide the ultimate step for the most dedicated weekend prospectors. The original dredges were barges sometimes the size of an apartment house. They were developed from harbor dredges used by the corps of engineers for clearing channels into American ports and they used scoops or buckets to rip up vast portions of river bottom.
They cost a small fortune and only the largest mining companies could afford them, but for many mining companies, especially in Alaska and on some of the larger rivers of the Pacific Northwest, they were literally worth their weight in gold. The barges often generated obscene profits with some generating hundreds of times their original purchase price over their careers. You might not be that lucky, but a dredge does offer an enormous technological improvement over simple sluices.
First, they can reach down and pull material off the bottom in spots where the water is simply too deep to dig and most today are also equipped with power sluices that allow you to wash gold even in water with no current. This means that you can hit spots that have not been as worked over and produce more gold even in spots that earlier prospectors have already worked hard.
The old time dredges usually used a dragline or a conveyor belt digger in shallow water, but today’s recreational dredges work on a completely different principal. Known as suction dredges, they are essentially vacuum cleaners. They suck up the gravel and sand from the river bottom and process it through a power sluice like this 2.5 inch Proline.
Suction dredges are easily the most efficient way for one or two men to mine placer deposits. However, you do need to check the regulations in the area you’re considering using your dredge, because the regulations vary. In general, dredges with an intake larger than 4 inches, like this 6 inch Keene is consider a commercial dredge on Federal lands, but in most places this 4 inch Proline is considered a recreational dredge.
One really great development in recent years is the development of the backpack dredge like the 2 inch Keene. It only weighs 65lbs and is designed to packed deep into the backcountry. Much of the gold produced in Alaska was mined from placers, often with the use of gold dredges, and today on state lands any dredge 6 inch or less is considered a recreational dredge.
In 1901 this Californian steam dredge was state of the art, but within a few years it would be small by comparison to the big Alaskan dredges.