Unlike the modern, small scale dredges; a bucket line dredge was very large. Instead of sucking up water and gravel through the use of water pressure, the bucket line dredges would scoop it up and run it through a long sluice box. Only 10 cents of gold was needed for each square yard of material to make a profit back when these dredges were common in the 1890s and on into the early 1900s.
Most people believe that gold mining in the Yukon and Alaska was primarily done with gold pans, or possibly sluice boxes. In fact, those methods were only used for testing streams, and in the early stages of mining in some areas such as the Klondike. Relatively little gold was recovered, and it wasn’t until the arrival of huge dredges that gold production soared.
Bucket line dredges, also known as draglines, are used to excavate both dry gravels and underwater gravels, but when employed at open cut gold placer mining operations, draglines perform the same function as bulldozers (i.e., stripping overburden, moving excavated material, stacking tailings, etc.)
They may be fitted with booms as long as 100 feet, which gives them a large digging radius. Although it costs less per unit to move materials using bucketline dredges, they are not as mobile as bulldozers. Bucket line dredges are fitted with buckets whose capacities range from 1/2 to 2 cubic yards that can gouge out several cubic yards of gravel on each pass, enormous amounts of material can be processed by a dredge, so even fairly poor ground could be profitably mined.
The bucket line dredges that changed the character of gold mining in Alaska and the Yukon were invented in New Zealand. Many changes and additions were made to make them suitable for working frozen ground, but the technology changed little for the 80 years they were in use. Although they look complex, the basic concept is very simple – the buckets scoop up the gravel and dump it into sluice boxes inside the dredge, water is pumped in to separate the gold from the gravel, and the worthless gravel is then dumped out the back.
Most modern dredges are much smaller, and use suction to bring up the gold-bearing gravel from river bottoms. Many are used by “recreational” miners due to their relatively low cost and ease of use.