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Diamond mining involves geological strategy, earthmoving, and winnowing. Most diamond mines are underground, and identifying a pipe opening or deposit is the first step. Open pit mining and underground mining are the two main ways to start a mining operation. Diamonds from underground chambers must be sieved for particulate matter before they are marketable. Alluvial diamond mining can be as simple as humans with winnowers, while sea-washed stones require more complicated procedures. Diamond mining jobs are often considered dangerous.
Diamond mining is a complex undertaking that typically begins with some degree of geological strategy followed by earthmoving and winnowing, either by mechanized forces or by individual manpower. Many of the deepest diamond mines in the world involve drilled shafts and automated diamond sorting and screening machines. More rudimentary operations may involve little more than individual miners armed with shovels and sieves. The process for mining diamonds from the sea or river is different when it comes to tools and processes, but still generally follows the same pattern.
Most diamond mines are underground. Diamonds are carbon compounds that form in the earth’s core when exposed to certain heat ranges from magma. They approach the surface as subterranean magma shifts, bubbles and responds to natural phenomena such as volcanic eruptions. Diamonds cool and harden in tunnels known as kimberlite tubes, which connect the Earth’s mantle to its crust. Most of the world’s diamond mining takes place in and around these pipes, although riverbeds and underwater kimberlite vents can also be fertile mining sites.
Identifying a pipe opening or deposit is always the first thing involved in diamond mining. Sometimes this is based on chance discoveries or past successes in a certain area. Usually, however, it is deduced on the basis of geological expertise. Geologists with specialized training in mine locating and mineral deposits will map suspected mines in the area. Crews typically will test the site by drilling samples that need to be examined in a lab for characteristics consistent with the presence of diamond ore.
On land, there are two main ways to start a mining operation. When diamond ore is believed to be relatively close to the surface, an open pit or open pit mine is usually excavated. This type of mine is what it sounds like: a deep, open hole, often streaked into multiple levels or steps, into which workers and moving stock descend. Most open pit mining involves a combination of heavy machinery and the work of diamond miners. Explosives and blasts are often used to speed up the process.
Underground mining is required if the pipe openings are deep below the surface. Wells are drilled with complex drilling machines, then tunnels, usually concrete, are built with openings parallel to the kimberlite pipes for easy access. Workers stay in the tunnels and scour the kimberlite deposits, usually by routing the tunnel contents onto conveyor belts or trolleys to bring them to the surface. This process is generally known as block caving.
Most diamonds from underground chambers must be sieved for particulate matter before they are marketable. There are various ways to sift through diamonds, but the most popular method involves a water rinse and agitation that takes place in or near the mine. Diamonds generally resist water, but stick to oil and grease. For this reason many sieves are coated with wax or other adhesive grease. All collected material is sifted through, and in most cases, the diamonds sink and stick while the rest of the debris is washed away.
Diamonds are also found in riverbeds in many parts of the world. Most of these deposits, which are called alluvial deposits, are more refined and easier to extract than those still present in the earth. In large part, this is because the earth naturally eroded the hard rock casings as they were dropped from pipes into streams. Alluvial diamond mining can be as simple as humans with winnowers, though more sophisticated efforts often involve basic machines like backhoes and sieves.
Stones that have been sea washed usually require more complicated diamond mining procedures. Diamond miners usually erect a modified seawall to protect the site, then remove most of the standing water, sift through the wet sand, and begin sifting. The farther it goes into the high seas, the more difficult it becomes and often specialist divers are involved. Divers are also sometimes employed in diamond mining in the underwater openings of kimberlite pipes, but this is typically more rare, as the costs involved are often very high.
Diamond mining jobs are often considered very dangerous. Some countries impose labor laws and workplace safety standards on diamond mines, but these are not ubiquitous and are not always followed even when they are in place. Sometimes environmental concerns and land restoration measures are also required, but again, adherence is not always as strong as the initial concern.
