How A Gold Trommel Works
Miners all over the world use gold trommels, they can be manufactured in any size to suit the needs of the miner and the claim. The purpose of a gold trommel is to separate the smaller gold bearing material from the larger substrate like rocks, pebbles and boulders. A trommel is a rotating cylinder with many holes of a given size, the holes act as a classifier, letting only the material smaller than the holes fall through while the rest of the substrates flow on out the other end of the trommel.
Example Of A Trommel Screen With Several Different Sized Holes For Classifying Material
To feed a trommel the gravel material is poured into a hopper at the front of the machine. The hopper may have some kind of a device like a metal grate to keep very large rocks and boulders from entering the machine. These are called grizzlies.
As soon as the material enters the hopper it is blasted with water to help break up clods and loosen the gold bearing particles from clays, roots, rocks etc.. As the material travels through the rotating drum it is continually sprayed with water. The action of the water and the rotating cylinder continue to break up the material so the smaller gold bearing particles can exit the trommel through the holes in the cylinder. The larger rocks pass on through the trommel cylinder. The smaller gold bearing particles that fell through the holes in the trommel cylinder are usually passed through at least one sluice box to trap the gold and further reduce the amount of non gold bearing material.
The Videos below show the rotating trommel and sluice box very well. You can see the holes in the trommel for the smaller gold bearing material to fall through. The water spray bar inside the trommel is visible and you can see the larger rocks exiting the end of the trommel.There is a sluice on the right side of the trommel that the finer gold bearing particles have been deposited into, the sluice captures the heavier gold and black sands while the lighter material passes on through the sluice.