Common Gold Concentration Methods, Part 1
There are a number of common methods for concentrating both placer and hard rock gold. Undoubtedly you are already familiar with some of these methods, but there are others you may not be aware of or that you you have only heard about in passing. So here are a few of the most common gold concentration methods:
This is simply a "fancy" term for crushing or grinding. Comminution is the first method of extracting and concentrating free-milling gold from host rock such as quartz. On a small scale this can be as simple as a miner crushing auriferous rock by hand, panning it to concentrate the gold, then extracting the same. In larger or commercially run gold operations comminution can take place on a massive scale using industrial crushers and grinders.
The simplest and most commonly used method of concentrating gold, gravity concentration is the "bread-and-butter" of every small-scale miner and prospector. Additionally, the tools and equipment involved in gravity processing should be well-known to all of us: panning, sluicing, dredging, drywashing, and so on. All of these methods use gravity (and gold's density and weight) to process, concentrate, and extract placer gold.
Amalgamation and Retorting
These concentration methods go "hand-in-hand" but at the front and back ends of the same process. They are typically employed in commercial gold operations as a means of concentrating every last gold particle and often employ dangerous materials such as mercury ("quicksilver" to the old timers) to bond or "amalgamate" these fine gold particles.
Retorting involves extracting the gold from the amalgam by "burning" it off using nitric acid or through the use of a heating and evaporation set up. CAUTIONARY NOTE: Burning off mercury from amalgam using nitric acid creates deadly cyanide fumes. Never attempt this in an enclosed space and make sure you wear appropriate protective gear such as a safety glasses or a full-face "splash" shield, and rubber or chemical gloves.
(c) Jim Rocha (J.R.) 2008