Print7.4.2: Hydraulicking or Hydraulic Mining
Hydraulic mining uses high-pressure water cannons, known as monitors, to dislodge relatively unconsolidated material. One of the earliest applications of hydraulic mining was to break down banks of alluvium containing gold and silver. These alluvial deposits are firm, but break down quickly upon the application of the water cannons. Of course, if digging the banks of alluvium were the goal, we could use wheeled front loaders or other traditional digging and loading equipment. The goal is not only to excavate the banks but to separate the gold, silver, or other metals from the sediments in these alluvial deposits. Toward that end, we use a gravity separation with water in a device known as a sluice. The sluice which is usually constructed, consists of a trough on a slight incline. The trough bottom may have embedded ridges. The idea is that the material laden water will flow gently down the sluice and denser materials will settle to the bottom. Toward this end, the material loosened by the water cannon is channeled to the sluice; and as it passes through the sluice, the heavier materials, e.g., grains of gold and silver, settle on the bottom of the sluice while the water and sediment are carried away.
Another important, but limited, application of hydraulicking is to break down mineral ores prior to slurry transport. Slurry transport is an important materials handling method in which a water-solid mixture is pumped over some distance. In some cases, the slurry may be pumped for 20 or 30 miles, while in others, it may be hundreds of feet. One such application is in phosphate mining. The overburden is removed, typically with a dragline, and then a monitor is used to break down the phosphate matrix into a slurry, which is then pumped to the mineral processing plant. We’re going to examine a case study in the next Lesson, and at that mine, they use a dragline to excavate the phosphate matrix and place it into a small pit where it is broken down and fed into the slurry pipeline. You’ll see some good pictures of hydraulic monitors in that case study.