If the ground is tightly cemented the buckets should not be too large, but should be smaller and strongly built. High-surface gradients might require additional bedrock to be dug or pond dams to be built. Coarse gravel that contained little fines, a good waste-disposal system, and careful advance made dredging possible. In one shallow relatively high value dredging operation in the Western United States, 52 inches of placer material was being excavated with a 3-cubic-foot dredge that drew 50 inches of water. For the same reason, if the ground is shallow, the slope of bedrock becomes a very important factor in pond depth and thereby in the size of the dredge. With a hull depth of 10 to 12 feet the pond beneath the dredge can cause flotation trouble. If the ground is shallow, 30 feet or less, a large dredge will have difficulty or cannot operate.

In general, if the ground is deep, if the gravel is not cemented, and if the property is large, the larger the dredge the lower the unit cost of mining. It is best not to assume that a dredge of standard design will suit all deposits.

If the results are generally favorable and suggest the probability of a profitable operation, then the next step is to test that thesis by a cost analysis to determine the optimum type and size dredge. Determining Suitable Dredge Size: After the placer deposit is properly prospected the miner has a reasonable knowledge of the volume and grade of the placer together with information on its geometry, formation, and the distribution of values by size and location as well as information on bedrock topography, surface topography, water supply, and a host of other information that is pertinent to future decisions.

Power jet gold dredge