Concentration is the process of eliminating much of the undesired mineral material that contains the gold. It is a vital part of reducing and even eliminating the need for mercury amalgamation.
Most methods of concentration rely on gravity. The density of gold is 19 times greater than that of water, which means it’s exceptionally heavy. For comparison, Mercury is 13 times as dense, and lead is 10 times as dense as water. Due to this fact, even a very small flake of gold will sink to the bottom of a body of water, making gravity an excellent method for concentrating liberated gold.
Current ASGM Practices
Sluicing is one of the most common methods of concentration. Water and crushed ore are combined and washed down a sluice lined with a fibrous material. The heavy gold sinks and is caught in the lining which is rinsed into a pan to be further concentrated, usually by panning.
Gold Panning is something nearly all of us have seen before. Gold-rich ore is combined with water in a shallow pan and gently swirled around.
The motion of the water lifts the lighter particulate matter which is allowed to escape over the rim of the shallow pan, leaving the heavier gold at the bottom of the pan.
Effective concentration of gold is challenging and requires the right materials and techniques. The majority of small-scale artisanal miners do not have the resources to attain or build an ideal set-up. Because of this, miners can lose 25% to 75% of their gold during concentration due to inefficient practices. This is evidenced by testing the tailings, which show a substantial quantity of leftover gold.
Improved Practices
Improved sluicing: Education on modern techniques for increased gold capture is needed, as is the dissemination of improved sluice design. MBMM has designed an improved gravity concentration sluice that has proven able to capture gold up to 300 mesh in size. We’ve offered the building schematics and consultation for the use of our sluices since 2007, and they’re still free to all. If you are interested in fabricating them or have questions, you can find out more at our website on the Improved Sluicing Technology page.
Shaker tables: This very effective gravity method uses vibration and water flow to separate particles by their weight. The undesired, lightweight materials, called gangue, are washed along the surface of the table, while heavier particulates remain to form a band of gold-rich concentrate. MBMM’s shaker tables feature custom-cut grooves and a subtle incline that guards against fine-gold loss and will retain 95% of free gold at >325 mesh, with customer reports of recoveries down to 425 mesh. To combat the elements and various environments in which gold is mined, our tabletops are fabricated from RPDM rubber which is exceptionally resistant to heat exposure. They are capable of running between *1 and 2.25 tons of ore/hour and can operate using *6-14 gallons of water per minute. Water can be recycled, so they can be operated in locales where water isn’t available by implementing a closed circuit system.
When gold is concentrated efficiently, yield increases, waste decreases, and the need for mercury amalgamation is rendered obsolete. This means a boost to the livelihoods of mining communities, which in turn supports personal, social, economic and environmental health.
*Numbers quoted reflect the capability range of our 4′ x 8′ and 5′ x 12′ shaker table models. Please see our website for more information.