Diamond mining is a complex endeavor that typically begins with some degree of geological strategy followed by earth moving and sifting, whether by mechanized forces or by individual manpower. Many of the world’s deepest diamond mines involve drilled shafts and automated diamond sorting and sifting machines. More rudimentary operations may involve little more than individual miners armed with shovels and sieves. The process for sea or river-based diamond mining is different when it comes to tools and processes, but typically still follows the same model.
Most diamond mines are underground. Diamonds are carbon compounds that form in the core of the earth when exposed to certain intervals of heat from magma. They move closer to the surface as subterranean magma shifts, bubbles, and responds to such natural phenomenon as volcanic eruptions. Diamonds cool and harden in tunnels known as kimberlite pipes, which connect the earth’s mantle to its crust. The majority of the world’s diamond mining activities happen in and around these pipes, though riverbeds and undersea kimberlite openings can also be fertile mine sites.
Identifying a pipe opening or deposit is always the first thing involved in diamond mining. Sometimes this is based on chance findings or past successes in a certain area. Usually, though, it is deduced according to geological expertise. Geologists with specialized training in mine location and mineral deposits will map out suspected mines in the area. Teams will typically then test the site by drilling samples that must be examined in a lab for characteristics consistent with the presence of diamond ore.
On land, there are two primary ways of beginning a mining operation. When the diamond ore is believed to be relatively close to the surface, an open pit or open cast mine is typically dug. This sort of mine is what it sounds like — a deep, open hole, often striated into several levels or steps, into which workers and removal supplies descend. Most open pit mines involve a combination of heavy machinery and diamond miner labor. Explosives and blasting are frequently used to expedite the process.
Underground mines are required if the pipe openings are deep below the surface. Shafts are drilled with complex boring machines, then tunnels are built, usually with concrete, with openings parallel to the kimberlite pipes for easy access. Workers stand in the tunnels and sift through the kimberlite deposits, usually routing the tunnel’s contents onto conveyor belts or trolleys to bring them to the surface. This process is usually known as block caving.
Most diamonds from underground chambers must be sifted from their particulates before they will be marketable. There are various ways of sifting diamonds, but the most popular method involves a water rinse and agitation that happens either at the mine or nearby. Diamonds generally resist water, but will stick to oil and grease. For this reason, many sieves are cased in wax or other adhesive grease. All of the collected material is flushed over the sieve, and in most cases, the diamonds sink and stick while the rest of the debris washes away.
Diamonds also occur in riverbeds in many parts of the world. Most of these deposits, which are called alluvial deposits, are more refined and easier to mine than those still lodged in the earth. In large part, this is because the earth has naturally eroded away the hard rock casings as they were tumbled from pipes to waterways. Alluvial diamond mining can be as simple as humans with sifting pans, though more sophisticated endeavors often involve basic machines like land-clearing backhoes and shovel sieves.
Stones that have washed out to sea usually require more complicated diamond mining procedures. Diamond miners usually erect a modified sea wall to protect the site, then remove most of the standing water, sift out the wet sand, and begin sifting. The farther out to sea this goes, the harder it becomes, and specialized divers are often involved. Divers are also sometimes employed in diamond mining at undersea kimberlite pipe openings, but this is typically rarer, as the costs involved are often very steep.
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. Environmental concerns and land restoration measures are sometimes also mandated, but again, adherence is not always as strong as the initial concern.