Placer mining is the process of recovering heavily eroded minerals (gold and other precious metals) from gravel or sand. Examples of deposits recovered through placer mining are the gold-bearing sands and gravel that settle out from rapidly moving rivers and streams.
Placer mining makes use of gold’s high density which causes the metal sink to sink quickly from moving water compared to lighter siliceous materials.
While the basic principles of placer mining haven’t changed since earlier times, the methods have improved considerably thanks to the use of modern mining equipment. Today, miners use a variety of equipment in their placer mining operations such as excavators, water pumps, and generators. Specific equipment used to recover gold and other precious metals includes gold wash plants, trommels, derockers, and sluice boxes.
Let’s discuss the basics of placer mining equipment so you can have a better understanding of how these machines work to acquire gold.
The four most commonly used equipment in placer mining
Placer mining equipment is designed to be durable and efficient when working in harsh environments. This gives miners the best chance to obtain gold and other precious metals from their operations. Let’s break down the four most commonly used placer mining equipment today.
- Gold Wash Plants
Gold wash plants come in many different options depending on the user’s mining needs such as gold placer plants, mining wash plants, and full production gold trommels, all of which are used for gold mining. These also include testing plants (aka portable trommel wash plants) coming from top global brands like MSI Wash Plants. Miners also have a choice between diesel-powered or gas-powered gold trommel wash plants to fit their specific needs and requirements.
Derockers are perfect for alluvial mining of gold and other precious metals in places where large boulders exist. Derockers, such as the RMS-Ross Derocker, offer a -5cm product to downstream recovery, and releases clean washed +5cm” rock and boulder separately. To further optimise placer mining operation, miners choose automatic dockers that are capable of self-cleaning, thus making the equipment more efficient.
- Sluice Boxes
Sluice boxes play an important role in any placer mining operations. Its basic design has stood for hundreds of years yet remains an effective way to recover gold from rivers and streams. Sluice boxes are also used to recover other precious metals and stones. Such equipment is mostly used in gold mining paydirt and sluicing creek beds where gold is aplenty. Gold dredge sluice boxes are also designed in various sizes depending on the user’s request and the amount of material they need to process.
Trommels (also known as rotary screens) allow miners to recover gold by filtering out large materials like rocks and boulders. Trommels come in many different sizes, with the most common ones being 45cm, 76cm, 121cm, and 2.1m. Most miners buy new gold trommels but it’s becoming increasingly common to purchase used placer mining equipment with refurbished parts to cut down on costs.
Companies like Savona Equipment are known for making excellent gold trommels and produce many different varieties of gold recovery equipment worldwide including gold trommel wash plants, mini wash plants, and portable gold trommels. Being such a big company has plenty of advantages as miners can order a custom made gold recovery wash plant to fit their specific needs and requirements.
How gold is extracted
The question now is, how does placer mining equipment work to separate gold from the sediment? Let’s discuss how each piece of equipment plays a role in placer mining operations.
Think of a trommel like a large, rotating sand screen. It’s set at an incline with lifter bars placed inside the tube. The process begins with feeding the materials into the upper end of the equipment. The pressurised water is then fed into the apparatus which combines flowing water and mechanical agitation to free gold from the bits of ore. The ore that passes through the trommel is further refined using a sluice box.
A sluice box uses the power of flowing water to collect gold. A typical sluice box measures around 3m long, 0.5 m wide and 25 cm deep, with a series of ripple in the bottom to help agitate the flowing water, thus helping to extract gold and nuggets the process. When a stream of water passes through the sluice box, the lighter waste materials are spilled out to one end to separate the gold.
To extract as much gold as possible, placer miners add mercury to their sluice boxes. Gold and mercury bond chemically to form an amalgam, which makes extraction that much easier. After the amalgam has been collected, it is heated in a crucible, breaking the amalgam and turning mercury into vapour. The gold can now be liquefied to remove any impurities.