In major mining operations, miners cannot simply stand knee deep in rivers and pan out everything like a "forty-niner." Instead, conveyor belts carry tons of quarried rock, stones and sediment from up stream or inside a mountain down to a screener separator. This is what the separator does to help sort the good from the bad, the chaff from the wheat and the gold from the gravel.
Vibration and Gravity
Screener separators often use vibration to separate larger rock from smaller grains and pebbles. Additionally, a "sloped screen" machine relies on gravity and vibration to separate various sizes of rock and sediment grains. A conveyor belt drops everything into a chute at the top, while the screened separator shelves shake, rattle and rock to move the smaller grains and dust to the bottom shelf. Then each shelf has an "out chute" that pours out the collected contents onto a series of layered conveyor belts or into mine carts, taking turns and dumping only one size of rock, pebble or grain into a cart.
How the Screener Separator Sorts out Gold
Gold is lighter than most of the rock surrounding it. It is this very principle that made panning for it so simple, since the water would wash away heavier minerals and rock sediment, leaving only the gold flakes and nuggets behind. The separator machines do the same thing. They shake down the gold nuggets and flakes onto the bottom screened shelf, where it sits until the mining company collects it, or it is dumped into a mining cart along the conveyor line and hauled away to be stored in a safe place.
How the Screens Separate Coal
Coal, while not especially heavy, is dense and chalky. It does not sift easily or well through a screener separator. It almost always will remain sitting on the top screened shelf of the separator. It is quite helpful in picking through and removing larger chunks of coal and placing the chunks in a miner's cart. Smaller chunks or tinier pieces that may be compressed in a factory into briquets is then dispensed through this shelf's "out chute" into a cart and rolled down to company storage until it can be emptied into a coal hopper and taken away by train.
Finding Precious Gems
It is entirely possible for these machines to find small gems, including diamonds. When these stones are discovered, the mining company can sell them to visitors or to jewelers. Mining companies may even use a screener separator to find chips of gemstones, of which amethysts are probably the most common.