The chart presenting the layer-depth of minerals is based on data collected by bottom cores. The whole water column is now contaminated with sediment particles, making it impossible to use standard bottom-detection methods such as echo sounders and boomers, which do not work in these environments. After separating out of minerals the transport medium (water) flows into the same dredging pit, rendering it slimy. As there is no good acoustic method available for finding out where the fallen sediment has settled, cleaning sweeps are not carried out. This slope regularly collapses, spreading material/sediment throughout the dredging pit and creating the possibility of damage to the material to be dredged. When dredging in a closed pit or pond the dredger often comes face to face with a steep slope. As soon as the layer holding the minerals is reached, the dredging process slows down, as separation of minerals now assumes maximum importance. When mining for pewter and gold the above-lying sediment layers are processed without mineral separation in order to achieve a higher production rate. Mining managers provide limitations (depth tolerances) to prevent damage and disruption to the dredging process and/or mineral separation. Detecting the right layer-depth and thickness of concentrate over the area to be dredged is difficult and time-consuming. Pewter is mostly found on a rocky bottom, while gold and diamonds lie on gravel layers. Most minerals, like rutile and zirconia, are to be found on top of a layer of clay with the highest concentrations found closest to it. This article describes some of the techniques used in these dredging operations and illustrates the importance of integrating techniques and information. The fact that the minerals are mostly covered in various sediments is one of the biggest problems in mining them. Dredgers float in a ‘wet environment’ where the surrounding water is used as transport medium. Dredgers involved in mining for (precious) minerals and metals often work in an inland dredging pit.
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