A diamond mine is an operation that extracts diamonds from the earth, either from their original volcanic source deep underground or from secondary deposits where rivers and ocean currents have carried them over millions of years. These mines range from massive open pits visible from space to underwater vacuums sweeping the ocean floor off the coast of Namibia. The scale is enormous: even a productive mine may process hundreds of tonnes of rock to recover a single carat of gem-quality diamond.
How Diamonds Reach the Surface
Diamonds form roughly 150 to 200 kilometers below the earth’s surface, where intense heat and pressure transform carbon into crystal. They would stay there permanently if not for rare volcanic eruptions that carry them upward through narrow, carrot-shaped channels called pipes. The two main types of rock that form these pipes are kimberlite and lamproite, both created from small pockets of molten rock deep in the mantle. As these melts race toward the surface, they pick up diamonds and other deep-earth minerals along the way.
Kimberlite pipes are the most common source of mined diamonds. The rock itself is a mix of carbonate, serpentine, and various minerals that cool into a distinctive blue-grey mass once they reach the surface. Lamproite pipes are rarer but can also carry diamonds. Both rock types formed from a shared source deep in the convective mantle, with differences in their mineral makeup reflecting how that source evolved over time beneath ancient continental cores called cratons. Southern Africa’s Kaapvaal Craton, for instance, has produced both kimberlite and lamproite eruptions spanning millions of years, with the location of eruptions shifting as the African tectonic plate migrated.
Not every kimberlite pipe contains diamonds. Geologists have identified thousands of pipes worldwide, but only a small fraction hold enough diamonds to justify mining. When one does, the pipe becomes the target of a primary diamond mine.
Open-Pit Mining
When diamond-bearing rock sits near the surface, miners excavate it from above, creating a progressively deeper pit. This is the most recognizable form of diamond mining. The pit expands in terraced layers, with trucks hauling ore and waste rock up spiraling roads cut into the walls. South Africa’s Jagersfontein mine, now abandoned, reached 275 meters deep using this method, and it holds a special place in the country’s mining history as one of the earliest large-scale operations.
Open-pit mining is generally the first stage of a mine’s life. It works well when the ore body is wide and accessible, and the ratio of waste rock to diamond-bearing material is manageable. As the pit deepens, though, the cost of removing overlying rock climbs steeply. At a certain depth, it becomes more economical to transition underground.
Underground Mining
Underground diamond mines pick up where open pits leave off, following the kimberlite pipe downward through tunnels and shafts. Operations can reach extraordinary depths. Jwaneng mine in Botswana, considered the deepest diamond mine in the world, extends to 625 meters and produces around 15 million carats per year. Koffiefontein in South Africa, discovered in 1870, reaches 620 meters, just five meters shy of that record.
At these depths, miners face intense heat, water intrusion, and the constant risk of rock collapse. The kimberlite ore is blasted loose, hauled to the surface, and then crushed. Fresh kimberlite, sometimes called “blue ground,” is hard and must be mechanically broken apart to release the diamonds locked inside. Weathered kimberlite closer to the surface, known as “yellow ground,” crumbles more easily and is simpler to process.
Alluvial and Marine Mining
Not all diamonds stay in their original pipe. Over millions of years, erosion breaks down the surface layer of kimberlite, freeing diamonds that wash into rivers, streams, and eventually the ocean. These secondary deposits are called alluvial deposits, and mining them looks completely different from excavating a pipe.
In riverbeds, miners remove sand and gravel to reach diamond-bearing layers underneath. In regions with distinct wet and dry seasons, digging typically happens during the dry months, and the gravel is sorted for diamonds when water is available for washing. Underwater dredges scoop material from stream bottoms, and after running it through a sluice to concentrate the heavy minerals, workers sometimes pick diamonds out by hand.
Marine mining takes this a step further. Off the coast of Namibia, diamonds that washed into the Atlantic over geological time now sit on the ocean floor. Specialized ships use giant vacuum systems to suck up sediment from the seabed, then process it onboard to recover stones. Namibian marine diamonds tend to be high quality because the journey from pipe to ocean naturally breaks apart flawed crystals, leaving only the toughest stones behind.
From Raw Rock to Rough Diamond
The ore that comes out of a diamond mine is overwhelmingly not diamond. A typical kimberlite deposit yields only a tiny fraction of a carat per tonne of rock processed, which means massive volumes of earth must be moved, crushed, and sorted for every small stone recovered. This is why diamond mines are among the largest excavation operations on the planet.
Once the ore is crushed, a series of separation techniques isolate diamonds from surrounding rock. Because diamonds repel water, one common method coats crushed material with a greasy substance that diamonds stick to while other minerals wash away. X-ray sorting machines detect the fluorescence diamonds emit and use air jets to push them into collection bins.
The rough diamonds recovered at this stage vary wildly. Expert sorters grade each stone based on weight, shape, transparency, color, and clarity. They also assess whether a crystal’s internal structure makes it suitable for cutting into a gemstone. Stones that pass these criteria become gem-quality diamonds destined for jewelry. Those that don’t, due to inclusions, odd shapes, or dark coloring, are classified as industrial diamonds and used in cutting tools, drill bits, and abrasives. The line between gem and industrial isn’t always sharp: “near-gem” stones fall in between and may be cut into lower-grade jewelry or specialty products.
Where Diamond Mines Operate
Diamond mines cluster in regions underlain by ancient, stable continental crust. Russia, Botswana, Canada, South Africa, Angola, and the Democratic Republic of Congo are the leading producers. Each region has its own character. Botswana’s Jwaneng mine is often called the richest diamond mine in the world by value. Russia’s Yakutia region in Siberia hosts several enormous open-pit mines carved into permafrost. Canada’s mines in the Northwest Territories operate in some of the most remote terrain on earth, accessible only by ice roads for part of the year.
South Africa holds a unique place in diamond mining history. The discovery of diamonds near Kimberley in the late 1800s launched the modern diamond industry. Koffiefontein, discovered in 1870, is still one of the deepest mines ever developed. The country’s Free State province alone has produced multiple historically significant mines, and the geological understanding of kimberlite pipes largely comes from studying South African deposits.
Environmental and Physical Scale
Diamond mines reshape landscapes on a dramatic scale. Open pits can stretch over a kilometer wide and hundreds of meters deep. Underground operations leave behind networks of tunnels that must be managed long after mining ends. Alluvial mining strips vegetation and topsoil from riverbanks, while marine mining disturbs seafloor ecosystems.
Modern mines are required to plan for rehabilitation from the start, setting aside funds to restore land after operations close. In practice, this means regrading pit walls, replanting native vegetation, and managing water quality in flooded pits that become artificial lakes. The effectiveness of these efforts varies widely depending on the country, the company, and the type of deposit being mined.