Editing Placer mining (section)

===Trommel===
[[File:Alaskan Trommel.jpg|thumb|Trommel at the Potato Patch, [[Yentna-Cache Creek mining district|Blue Ribbon Mine]], Alaska]]
A [[trommel]] is composed of a slightly inclined rotating metal tube (the 'scrubber section') with a screen at its discharge end. Lifter bars, sometimes in the form of bolted in angle iron, are attached to the interior of the scrubber section. The ore is fed into the elevated end of the trommel.  Water, often under pressure, is provided to the scrubber and screen sections and the combination of water and mechanical action frees the valuable heavy minerals from the lighter gravel. The mineral bearing ore that passes through the screen is then further concentrated in smaller devices such as sluices and jigs.  The larger pieces of ore that do not pass through the screen can be carried to a waste stack by a conveyor.