Regardless, if we have a body of water covering a placer deposit, we will consider strongly using dredge to recover the minerals of interest. As we will see, hydraulic mining may be used in these deposits as well. Although these terms may be used interchangeably with dredging or dredge mining, you can’t assume that to be true in all cases. I mention this here because you will sometimes hear or read about placer mining or alluvial mining.
These alluvial deposits created by glaciation, are also known as placers. Glaciers once covered a significant portion of the Earth’s surface, and the movement of these glaciers created extensive unconsolidated deposits of materials containing not only sand and gravel, but gold, tin, diamonds, and other heavy minerals. Dredging to remove this material has the additional benefit of deepening the channel or harbor, and sometimes that is the primary purpose of dredging, and the recovery of minerals is a secondary benefit… the “icing on the cake,” so to speak! Gravel can be used sometimes in concrete as well as for a variety of other purposes such as architectural and landscaping purposes. The bottom of rivers, lakes, and harbors is often a good source of gravel. Shortly, we will look at how the payload is moved in a little more detail, but for now, let’s talk for a moment about the kinds of materials that are typically recovered with this method, dredging or dredge mining. Simplistically, the dredge is designed to lift these materials of interest from the bottom up into the dredge. We need to add one more condition, and that is: the material of value on the bottom must be unconsolidated, such as sand and gravel, or it must be very soft.
Of course, the only reason for floating a dredge is to recover something of value at the bottom of this body of water. In many cases, this is a natural body of water such as a river or a lake, but in others, it is a manmade pond or small lake. Accordingly, a dredge requires a body of water in which to operate. A dredge is the principal piece of equipment used in the dredging method and, essentially, a dredge is a boat containing specialized mining and materials handling components.
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