Galeries du Diamant
The-geology-of-diamonds

Mining Diamonds

In the last installment of the Galeries du Diamant Journal, we discussed the important, costly, and time-consuming process of locating a cache of naturally-formed diamonds and determining whether or not it would be cost-effective to dig. Though those steps are vital, of course, the next set of steps is equally important: digging down, finding the diamonds, bringing them up to the surface, and releasing them from the rock. In today’s journal, we’ll explore everything this process entails.


Open-Pit Mining
As we discussed in the last GD Paris journal entry, the stones in which diamonds are encased when they are pushed up to the crust from the mantle are called kimberlites. When a volcanic eruption occurs and kimberlites travel upward with the force of the magma, the paths they follow are (appropriately) called “kimberlite pipes.” These kimberlite pipes are the sites where mines are dug, because they have the greatest density of rough diamonds. When it has been determined that a kimberlite pipe has a large enough volume of quality diamonds to be lucrative, digging can begin.
When one imagines a mine, the picture that typically comes to mind is one of a labyrinthine underground passageway – but that more accurately describes the goldmines of the American west or the limestone mines beneath Paris. Diamond mines are often characterized by immense holes in the ground. When a kimberlite pipe is discovered, digging begins from the surface and descends vertically and outwardly to create a pit from which raw kimberlite stones can be extracted.
The “Big Hole” is a former diamond mine in Kimberley, South Africa (from which the term “kimberlite” derived). It has the distinction of being the deepest hand-excavated pit in the world, at 240 m deep. Though it is no longer in operation as a diamond mine, it is now a museum.

The Big Hole Kimberley Mine, South Africa

The Big Hole (Kimberley Mine), South Africa

Underground Mines
This type of mine is much more similar to the image of an old-West mine winding around beneath the earth’s surface. In some cases, this can be safer and more practical, particularly as the digging process goes deeper and deeper into the Earth. Ironically enough (considering how deeply within the earth diamonds are actually formed) diamond deposits are often denser where kimberlite pipes open to the surface. For this reason, open-pit mining is logical – down to a certain depth. However, as one descends deeper below the surface and diamonds get sparser, it’s difficult to justify expanding an ever-growing pit. Simply cutting a tunnel into the earth and extracting diamonds that way is much more logical and less dangerous.
Tunnel mining is often combined with open-pit mining, and tunnels are dug out from the pit into the surrounding stone.

Extracting Kimberlite from Mines
Much as kimberlite was long ago blasted upward out of the earth’s mantle via natural explosions, kimberlite is now loosened from the earth’s crust by man-made explosions. Large amounts of rock are blasted away, and they are not tested for diamonds on-site. Instead, they must be hauled up and brought to a separate location for processing and extracting diamonds.
Huge trucks and steam shovels haul away literal tons of dirt, but the concentration of actual diamonds found in the rocks is deceptively small. The actual density of carats of diamond per ton of dirt varies from site to site, but .5 carats of diamond per ton is considered acceptable – to put that into perspective, that is a mere .01 grams of diamond per 2,000 pounds of earth, or approximately one part diamond to one hundred million parts earth.

Alluvial Mining
Much as water wore away the Grand Canyon over millions of years, water can wear away and loosen diamond-containing kimberlite. Alluvial mining – often called “artisanal mining” because of the nature of the operation and the quality of the stones yielded – means finding deposits of kimberlite where they have been transported by rivers and streams. The distance from the actual kimberlite pipes means a lower yield and a distribution over a larger area, so this method does not lend itself to industrial diamond mining.
Though this article focuses heavily on the more industrial forms of diamond mining, it is also vitally important that we address artisanal mining – which, as will be explained later, is particularly important to GD Paris.

Alluvial Mining Diamonds

Alluvial Mining Rough Diamonds retrieved by artisan miners in Liberia for Galeries du Diamant

Extracting Diamonds from Kimberlite
The mission of mining diamonds is to extract kimberlite stones from the earth’s crust – but even once the kimberlite is extracted, the work is far from done. The actual diamonds themselves must be removed from the worthless stone surrounding them. This is a multi-step process.
First, the kimberlite must be crushed into smaller, more manageable pieces – but carefully, so as not to damage any diamonds inside. Ferrosilicon, a silicon-iron mixture (or more simply put, a conveniently magnetic sand) is used to wear away the less-hard material surrounding the diamonds, then is extracted by magnets. One is left with diamonds and a few other lingering stones, and an x-ray can be used to separate the two.

The State of a Rough Diamond
Even when a diamond is removed from the surrounding kimberlite stone, it still hardly resembles the beautifully cut and polished final product that ends up adorning a piece of jewelry. Rough diamonds occur in all sorts of shapes, but they are much more organic than they are geometric. In fact, when looking at a diamond that has just been separated out of kimberlite, it is hard to see the potential it has to become something breathtaking.
Diamond “cutting,” the process by which rough diamonds are shaped into the complex and beautiful shapes to which jewelry collectors are accustomed, is an art. Tools like diamond saws and lasers are employed to shave off excess material and create perfectly straight planes. This work must be done by an expert who has lots of experience – every cut matters and will affect the sparkle of the diamond.

The more one explores the process that goes into mining, extracting, and shaping a diamond, the more apparent it becomes that hours upon hours of effort by both man and machine are required to produce a market-ready diamond. For GD Paris, every step of the process is equally important. It is our mission to oversee the journey of each and every diamond from the day it emerges from the ground to the day it is first held in a collector’s hand. As the journals progress, it will become more and more evident how important this is – and how much it sets us apart.

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