Placer mining is often used for precious metal deposits (particularly gold) and gemstones, both of which are often found in alluvial deposits of sand and gravel in modern or ancient stream beds. Placer mining uses only water, no chemicals, for mineral extraction or separation.
A placer gold mining machine, also known as gold trommel, is used worldwide for the majority of placer mining activities. The purpose of a gold trommel is to process the gold-carrying material by separating the bigger boulders and rocks and allowing the smaller material to go through a sluice box.
This smaller material is the part that contains the gold. This is called free gold as it is not encased in the rock itself. Free gold ranges from fine grains, to flakes and even small nuggets.
The entire operation is referred to as a wash plant.
The Gold Trommel
A gold trommel may look like a complicated piece of machinery but it is actually simple to build, and it comes in a variety of sizes.In some cases, where they have bigger wash plants, a grizzly is usually set up directly above the hopper where material is first loaded into the wash plant. Depending on the type of material you are feeding into the hopper and the quality of trommel itself, the material is dumped onto the grizzlyto separate the largest boulders which could damage the trommel. This also allows the system to work at its highest capacity.
A vibrating screen deck is sometimes, used with, or instead of a trommel. Breaking Down the Material
Once the gold-containing material is put into the hopper where jets of water wash it down to break up the material and extricate the gold. These water jets wash the bigger rocks and break apart any mud and clays that could contain placer gold and stop it from Being recovered.
Then the smaller gravels (containing gold) flows into the rotating drum of the trommel to break apart the material even more. The hopper also has a variety of water jets inside to break apart any hint of dirt and clays.
The rotating drum is made with a special screen substance that allows the smaller gravel to get through to a sluice box while the bigger rocks go into the drum and then get expelled. Depending on the roughness of gold in the location, the ideal screen size could be a half-inch or one-fourth of an inch.
The Sluice Box
It should be noted that the trommel itself doesn’t sift out the gold. It just facilitates the separation to create finer sediments so that the gold is heavier than the rest of the material. It is then run over the sluice box where the heavier gold is captured.
Sluice boxes are designed to mimic naturally occurring gravity separation. As water carries gold-laden sediment through the box, small obstructions called riffles block the free flow of material. These tiny flow restrictions form low pressure pockets where the heavier gold drops and collects.
The sloping angle of the trommel and the sluice box is very important. So is the flow of water. When the trommel is operating properly all finer material will have time to fall through the screens and all the clay and sediments will be washed off the bigger rocks. The angle of the sluice box and water flow creates the pressure and allows just enough time for the heavier gold to be captured in the riffles while the remaining sediments washes away.
But are We Making Money?
Placer miners generally refer to the gold value of their ground in terms of dollars per yard. At today’s prices, $13 per yard material or “$13 Rock” would only have to contain ¼ gram of gold. This would probably be about the minimum for a profitable operation depending on stripping of overburden, haul distance and the efficiency of the wash plant.
2 people and a front-end loader are required to run a trommel effectively if the wash plant is located right next to the deposit. One person feeds the material into the grizzly while the other oversees the trommel’s operation, ensuring everything works perfectly. However, most operations require a huge bulldozer for stripping, at least one truck for hauling and the operators. Fuel is a big expense at any mine. With today’s operating costs, a larger operation would likely require $20 Rock to make money.
You can see all the trials and tribulations of placer mining on the amazing Discovery Channel show Gold Rush.
This article contains the author's opinions. These are not investment-related recommendations. Do not consider the article as any type of commercial solicitation or an investment product offer.
About the Company
ELY GOLD ROYALTIES INC.(TSXV: ELY, OTCQB:ELGYF) is a Vancouver-based emerging royalty company with assets focused in Nevada and the Western US. Its current portfolio includes 33 Deeded Royalties and 21 Properties being sold to retain royalties. Their portfolio includes three producing royalties and is currently generating significant revenue.
Ely Gold’s royalty portfolio includes producing royalties, fully permitted mines, mines under construction and development projects that are being permitted for mine construction.