The Mir kimberlite pipe is a diamond quarry in Yakutia. How are diamonds mined?

These elegant, outwardly fragile, incredibly beautiful stones with the ability to reflect and refract rays, scattering magical sparks of light around them, were once thrown through volcanic vents onto the surface of planet Earth. In our time, these volcanoes have long been extinct, their above-ground part as a result of erosion processes has disappeared without a trace, but the rocks, stones and other substances frozen in the crater have not disappeared anywhere.

Scientists learned that these vents contain a huge amount of diamonds only in the middle of the last century, when a huge diamond deposit, nicknamed the kimberlite pipe, was found on the territory of the African continent (it was later discovered that such natural formations contain about 90% of natural diamond reserves planets).

People could not ignore such an event - and active searches for such deposits began all over the world. Some countries, such as Botswana, Russia, Canada, South Africa, Angola, were lucky, and having discovered the desired rock, they almost immediately began to develop promising finds, digging a deep hole and creating a huge crater.

Subsequently, scientists noticed an interesting feature of such holes: it is extremely dangerous for helicopters and other aircraft to fly over man-made craters, since the huge hole literally sucks them into itself.

Education

As for the process of formation of a kimberlite pipe and diamonds in it, it looks quite interesting. Several billion years ago, a breakthrough of magmatic solutions and gases occurred in the bowels of the earth (and it is interesting that it did not happen in a thin part of the earth’s crust, the thickness of which is about 10 km, but the explosion pierced a powerful platform 40 km thick).

As a result, a conical-shaped channel appeared, more similar to a champagne glass: the deeper it goes underground, the narrower it becomes and at a certain depth it turns into a vein.

The crater opening of this channel is usually from five hundred meters to one and a half kilometers. After the eruption, breccias (volcanic fragments) and gray-green tuff, the so-called kimberlite, were frozen in the crater of this crater - a rock consisting of phlogopite, garnet, olivine, carbonates and other minerals.

When these minerals reach the earth's surface by other means, their form is always well-cut crystals. But in the composition of kimberlite there are no such faces, and the grains are round in shape. As for diamonds, they appear on the surface in a ready-made form with sharp edges that can be used to cut glass without processing.

Despite the fact that a kimberlite pipe is usually 10% filled with gems, extracting diamonds from the rock is a rather labor-intensive process, since only about 1 carat of gems, which is 0.2 g, is extracted from one ton of kimberlite.

The first kimberlite pipe, called the “Big Hole,” was found in the mid-19th century. in South Africa, in the Kimberley province (where the name of both the diamond-containing rock and the vent itself came from). This deposit is also the largest quarry that was created by people without the use of any technology.

To create a hole of such a scale in the earth's crust, more than 50 thousand miners were involved, who developed the quarry using shovels and picks. As a result, over fifty years, more than 22 million tons of soil were extracted from the bowels of the earth and more than 2.7 thousand kg of diamonds (about 14.5 million carats) were extracted.

Despite the fact that at the moment the “Big Hole” deposit has completely exhausted itself, the diamond quarry still remains a local attraction, since for more than a century it has held the glory of the largest man-made hole in our world: its area is about 17 hectares, along the perimeter the hole has 1 .6 km, and the width is 463 m.

As for the depth, at present it is not very great, but previously it went down to 240 m. When diamond mining stopped, the deposit was filled up to 215 m, after which underground streams filled the bottom of the quarry with water and created a lake. Currently the hole is 40 m deep.

Quarry "Mir"

In the middle of the last century, on the territory of Yakutia in Russia, geologists found several kimberlite pipes at once - the first was “Zarnitsa”, discovered in 1954. Few gems were found in it, but the discovery of this vent prompted geologists to continue the search work.

And as it turned out, not in vain: the very next year, one of the largest diamond deposits of our planet called “Mir” was discovered in these parts (on the map you can find it near the city of Mirny at the following coordinates: 62°31'42″N. latitude 113°59'39″E). It is noteworthy that it was here that the largest gem in Russia, called “XXVI Congress of the CPSU,” weighing 342.5 carats (that’s a little more than 68 grams) was found.

The country's authorities paid great attention to the development of this Mir kimberlite pipe, attracted a huge number of people - and after some time, among the wild and uninhabited region, first a village was built, and then the city of Mirny, located more than a thousand kilometers from Yakutsk. The settlement was immediately placed so that the kimberlite pipe was right next to Mirny.

Work on the development of the Mir deposit in permafrost conditions (in winter the temperature here is often -60°C) was extremely difficult - it was very difficult to work with the earth and the soil had to be undermined with dynamite. Within a few years, the quarry produced about 2 kg of diamonds per year, of which 20% had jewelry value, and the rest were used for industrial purposes.

At the moment, it is believed that the Mir quarry produces the largest amount of diamonds in Russia and a quarter of all diamonds on our planet (and this, despite the fact that in size it is still somewhat inferior to another similar deposit found in these parts - the kimberlite pipe “Udachnaya”): its diameter is 1.2 km, and its depth is 525 m.

Several years ago, diamond mining in the quarry was stopped after the depth of the hole reached critical dimensions, and all work moved to the Mir underground mine. Working underground is difficult in itself, and in this case it is further complicated by the fact that underground water constantly floods the mine, as a result of which it has to be constantly pumped out and directed into natural faults that were found in the earth's crust.

Work in the Mir kimberlite pipe is not going to be stopped in the near future, since geologists have discovered that a huge amount of diamonds lie at a depth of more than one kilometer, and therefore the Mir deposit can be developed for more than thirty years.

Quarry "Udachnaya"

The largest kimberlite pipe in Russia is also located in Yakutia, 20 km from the Arctic Circle (on the map it can be found at the following coordinates: 66°25′ N 112°19′ E). Its parameters are:

• Width – 2 thousand m;
• Length – 1.6 thousand m;
• Depth – 530 m.

This hole actually consists of two pipes adjacent to each other - Western and Eastern. In terms of their characteristics, gems from different vents are quite different from each other.

Despite the fact that this diamond quarry was opened in the mid-50s, it began to be actively developed only in the early eighties. Currently, gems are mined in an open-pit manner, but since the depth of the deposit has become critical for this type of mining, an underground mine has recently begun operating here.

Experts say that most of the diamonds from the Udachnaya Kimberlite pipe have already been removed from the bowels of the earth, and some of the finds are amazing. For example, a stone was recently found here containing about 30 thousand diamonds, which is a million times higher than their usual concentration.

Doctor of Geological and Mineralogical Sciences, Professor A. PORTNOV.

From kimberlite pipes alone (not counting alluvial deposits) on Earth, up to 20 tons of industrial and jewelry diamonds are mined annually - worth 6-7 billion dollars. The lives of tens of millions of people are in one way or another connected with the search, extraction, processing, and sale of diamonds. Diamonds (diamonds) are not only precious jewelry. The use of diamond tools more than doubles the economic potential of any developed country. Diamonds have been mined for many centuries. And to a simple question: how are they formed in nature? - there is still no answer. It is generally accepted that diamonds crystallized deep in the bowels of the Earth - in the mantle, and the so-called kimberlite "explosion tubes" carry them to the surface of the planet. In this explanation, almost everything is incomprehensible: both the mechanism of diamond formation and the reasons for the appearance of kimberlite pipes, rooted in the unknown depths of the Earth. The hypothesis proposed here is based on the facts accumulated by modern geology and reveals new ways to solve these issues.

Kimberlite pipe "Mir", western Yakutia. A huge cone filled with diamond-bearing rock that broke out of the mantle through a narrow “puncture” under very high pressure of hot gas.

Next to the rounded deep-seated minerals, the diamond crystal especially stands out and attracts attention with its perfectly regular shapes.

Kimberlites are mantle rocks with numerous inclusions of pebbles - deep-seated minerals, rounded by gas flows.

The mineral apatite, rounded by mantle gases, looks almost no different from ordinary river pebbles.

Many types of deep pebbles, although they are very similar to ordinary ones, have a special rough surface - “shagreen”. This photo shows a pebble of the titanium mineral ilmenite with a shagreen surface.

“Shagreen” is also characteristic of olivine grains, one of the main minerals of the mantle.

At high magnification (2000 times) it is clear that “shagreen” is a special corrosive surface. It is formed when exposed to hot gas.

Three mysteries of kimberlites

Thousands of scientific articles are devoted to diamonds and diamondiferous rocks of the mantle - kimberlites. But they do not answer the three main mysteries of primary diamond deposits. First: why are kimberlite pipes located only on ancient shields and platforms - the most stable and stable blocks of the earth's crust? What monstrous forces could force the heavy rocks of the Earth's mantle, seemingly contrary to Archimedes' law, to rush upward and break through a layer tens of kilometers thick of lighter rocks - basalts, granites, sedimentary ones? And why do kimberlite pipes “pierce” the thick 40-kilometer crust of the platforms, and not the much thinner 10-kilometer crust of the ocean floor or transition zone - at the border of continents with the oceans, where hundreds of smoking volcanoes and free lava are located on deep faults pours out to the surface? Geologists have no answer to this question.

The next mystery is the amazing shape of kimberlite pipes. After all, in fact, they do not look like “pipes”, but rather like champagne glasses: a cone on a thin stem that goes to great depths. Geologists have been habitually calling them “explosion tubes” for a hundred years now, without thinking about how absurd this phrase is. After all, explosions in a homogeneous medium do not form tubes at all, but spheres. Numerous so-called “camouflage chambers” have now been drilled - voids left after powerful underground nuclear explosions. All these cameras are spherical in shape. But kimberlite cone pipes also exist! And, apparently, the secret of the birth of diamonds is connected with their formation. How did they come about? There is no answer to this question yet.

The third mystery concerns the unusual shape of mineral grains in kimberlite rocks. It is known that the minerals that crystallize first from molten magma always form well-cut crystals. These are apatite, garnet, zircon, olivine, ilmenite. They are also widespread in kimberlites, but for some reason they do not have crystalline edges, the grains are rounded and resemble rounded river pebbles in shape. Geologists are trying to explain this mysterious feature by saying that the minerals were melted by hot magma. But melting, as is known, leads to the transformation of crystalline minerals into amorphous glass, devoid of a crystalline structure. However, no one was able to detect any traces of “vitrification” or loss of crystalline structure in these rounded grains.

At the same time, diamond crystals, which, according to current concepts, originated in the mantle and were carried out in finished form along with kimberlite magma from a depth of 150 to 600 kilometers, are presented at enrichment factories as whole mountains of sparkling, ideally shaped octahedra with sharp edges, which are so convenient for cutting glass! These sharp edges have been preserved despite the fragility of diamond crystals and their ability to easily split along certain planes. It turns out that diamond crystals, having gone through a long and thorny path along with molten magma, look as if they had just come off a factory assembly line. And the crystals of zircon, apatite and other minerals (it is believed that they separated from the melt directly in the tube) lost their edges. How to explain such a paradox?

Kimberlite pipes - "chimneys" of the mantle

Extensive analytical and experimental material allowed the author to construct a new model for the formation of kimberlite pipes and diamonds. It explains many of the geological mysteries associated with these ultra-deep formations. The model is based on extensive information about the gaseous, predominantly hydrogen-methane, “exhalation” of the mantle, and possibly the Earth’s core.

In my opinion, kimberlite pipes are traces of a “puncture” of the lithosphere by huge gas bubbles rising from the mantle. Such a bubble, trying to break out to the surface of the Earth, makes a thin, “needle-like” exit through the hard crystalline rocks of the platform’s foundation, and only then an expansion is formed in the soft sedimentary rocks - a “glass”. Deep gas pushes them apart with terrible pressure of tens of thousands of atmospheres, transmitted from the mantle to the upper part of the earth's crust. The gas flowing through the “needle” puncture is triggered in approximately the same way as the pressure transmitted through the tubes of the oil hydraulic drives of a car.

The confinement of kimberlites specifically to platforms is explained by the fact that they are almost gas-tight. Therefore, tiny gas bubbles scattered in the rocks accumulate under them, which combine into large bubbles of hydrogen-methane composition. At a certain critical volume, such a bubble begins to gradually “float”, that is, penetrate into the structure of the platform and rise to the surface of the planet.

The platforms look like saucers floating in an aquarium, with air bubbles rising from the bottom. The bubbles flow around the saucer, but some of the gas accumulates under its bottom. Gas rises from the mantle, as evidenced by the fact that helium here is sharply enriched in the light, deep-seated isotope of helium. But in the underground gases of platforms there is a thousand times less such helium than in the gases of volcanoes. Consequently, the platforms are a dense “plug” for mantle gases.

Scattered mantle gas is collected into large bubbles due to the powerful influence of so-called hot spots (geologists learned about their existence relatively recently) - deep “nozzles” burning the lithosphere from the inside. For example, one of these modern hot spots burned through the thin crust of the Earth in the Pacific Ocean, and then the volcanoes of the Hawaiian Islands arose. The same “nozzle” worked in the same place 70 million years ago and also left its mark on the ocean floor - a “seam” of solidified basaltic lava, a giant underwater Imperial Ridge stretching from the Aleutian Islands to the Hawaiian Islands.

Volcanoes are like active “chimneys” of the Earth. They work properly if there are no “dampers” in the way of the gases emitted by them. Most often, moving platforms become such obstacles. They are usually so powerful that the hot spot does not have enough energy to burn through it. But it is enough to melt rocks at depth and collect the gases scattered in them into huge bubbles.

As you know, tiny droplets of fat in milk do not float until the energy of the butter churn produces a large enough lump of butter. So it is here. When large gas bubbles form under the platforms, Archimedes' principle comes into force. The density of the gas mixture (hydrogen-methane), even at mantle pressure, will be less than the density of water. But the density of the mantle itself is more than three times the density of water. This means that the lifting force of a bubble with a volume of 1 cubic kilometer will be 2.5 billion tons! And besides, this gas is heated to 600-800 o C.

The fact that the kimberlite pipes at depth are narrowed into a thin stalk suggests that the entire enormous lifting force of the gas was applied to a very small area. At the same time, tens of kilometers of rocks were as if pierced by a giant needle. This formed a thin channel 100-150 kilometers long. The gas bubble was squeezed up along it until it penetrated into the soft rocks of the platform’s sedimentary cover. We can say that the mantle, as it were, “inserts an enema” into the thick earth’s crust: soft sedimentary rocks move apart, forming a cone of a kimberlite pipe.

As the gas bubble floats upward, it creates a low-pressure zone at its tail. Mantle rocks recrystallized under the influence of gas are crushed and rush into this zone, into a thin breakdown. The gas drags the mantle rocks with it. As if in a giant sandblasting machine, grains of minerals rush in the hellish convection currents of a gas mixture that geologists call fluid. In this case, the crystals are peeled off, lose their crystalline edges and turn into deep pebbles of a gas flow, almost indistinguishable from ordinary river pebbles.

But there are still differences - they are clearly visible under a microscope. Under the influence of hot gas jets, a special surface of kimberlite minerals is created. Experts call it "shagreen". When magnified thousands of times, it looks like a microporous corrosion structure. The surface of meteorites or gas turbine blades is approximately the same.

Diamonds - "soot" of the mantle

But why are the diamond crystals mined in kimberlite pipes so beautifully cut? After all, it is believed that magma pulled them out of the “stone caves” of the mantle and dragged them more than a hundred kilometers!.. Of course, diamond is the hardest mineral, but even this cannot save it. After all, it is known that placer diamonds are rounded and chipped, since this mineral is quite fragile.

Countless textbooks show diamond-graphite equilibrium diagrams and say that diamond arises from graphite. But for some reason no one asked the question: where does graphite come from in the mantle?.. After all, it is unstable there, and it is called a “forbidden” mineral for mantle conditions. Carbides are a different matter. They are stable here: carbides of iron, phosphorus, silicon, nitrogen, hydrogen. Hydrogen carbide is a gas, ordinary methane, it is mobile and easily concentrated in deep fluid.

At one time, geologists did not attach importance to the remarkable discovery of the Soviet physicist B. Deryagin, who back in 1969 synthesized diamond from methane and, what is very important, at a pressure even below atmospheric. Even then, this discovery should have radically changed the existing ideas about diamond as a mineral that necessarily crystallizes from melts and at high pressures. B. Deryagin's data allowed me to consider the possibility of diamond crystallization from a fluid, a gas mixture in the C-H-O system.

It turns out that in such a fluid, oxygen at ultra-high mantle pressure loses its oxidizing properties and does not even oxidize hydrogen. But when gas rises upward, when a kimberlite pipe is formed, the pressure drops. It is enough to reduce the pressure 10 times - from 50 to 5 kilobars - for the activity of oxygen to increase a million times. And then it instantly combines with hydrogen and methane. Simply put, the gas spontaneously ignites - a furious fire breaks out in an underground pipe.

The consequences of such an underground “fire” depend on the ratio of carbon, hydrogen and oxygen in the fluid. If there is not too much oxygen, it will remove only hydrogen from the methane molecule (CH 4). The resulting water vapor will be absorbed by mineral dust and form serpentinite, the most characteristic mineral of kimberlites. Carbon, remaining “lonely”, at a pressure of thousands of atmospheres and a temperature of about 1000 o C, will close with unsaturated valence bonds “on itself” and form a giant molecule of pure carbon - a diamond! In practice, such a favorable combination of components in a gas mixture is rare: only five percent of kimberlite pipes are diamond-bearing.

More often it happens that there is either too much oxygen to form a diamond, or not enough. In the first case, carbon will burn and turn into gases - oxides: CO or CO 2. Then barren kimberlites appear. They are characterized by increased magnetism because they contain iron oxide - magnetite. There was a lot of oxygen, and it “snatched” the iron from the silicates. If there is a deficiency of oxygen or methane, only water vapor will appear, and it will be absorbed by serpentinite. It turns out that diamond arises as a product of spontaneous underground combustion of carbonaceous fluid. Diamonds are analogues of ash or soot settled in the “chimneys” of the mantle!

The combustion of methane increases the activity of oxygen and affects the isotopic composition of carbon and nitrogen that make up diamonds, since heavy isotopes are concentrated in the oxidizing environment.

Growing diamond crystals capture numerous dust inclusions from the gas - tiny grains of minerals from the surrounding rocks. The age of these mineral inclusions sometimes coincides with the geological age of kimberlite pipes, but more often the inclusions turn out to be much older. For example, in the diamonds of the famous Kimberley pipe (South Africa), which penetrated into the surrounding rocks 85 million years ago, the age of pyrope garnet inclusions (determined by the samarium-neodymium method) is 3200 million years. In the Yakut Udachnaya pipe, which broke through the surrounding rocks 425 million years ago, the age of clinopyroxene mineral inclusions (determined by the potassium-argon method) is 1149 million years.

Based on such data, geologists usually conclude that diamonds crystallized in the mantle, perhaps billions of years ago, and then were thrown to the surface of the Earth by an explosion. In my opinion, the inclusions in the diamonds were captured by growing crystals from the "dust" of the gas flow surrounding them.

In recent years, sophisticated methods of analysis have made it possible to identify native metals among inclusions in diamonds - iron, nickel, chromium, silver, as well as nickel and iron sulfides. How did they get into diamonds? In my opinion, all these metals were reduced from deep rock minerals - silicates with high content of iron, nickel, silver and oxides with high chromium content - such powerful reducing agents as hydrogen and CO, and deep hydrogen sulfide converted some of these metals into sulfides. The diamond "armor" preserved this unstable sulfide-metal dust in crystals.

For a long time, sharp “dry” contacts of kimberlite pipes with surrounding rocks remained a mystery to geologists. Geologists know that around massifs of igneous rocks of all types, powerful zones of contact changes arise due to recrystallization and changes in the host rocks. But at the contact with kimberlites, changes in sedimentary rocks are negligible. It turns out that there are changes, and very significant ones, but they are of an unusual nature. Around the tubes, powerful - up to half a kilometer - halos of concentration of small grains of luminescent minerals appear.

The content of apatite and zircon grains - minerals that glow brightly in ultraviolet rays - increases tens and even hundreds of times here. Moreover, apatite glows not with the usual yellow, but with a bluish light, which is characteristic of kimberlite apatite. These luminescent halos are explained by the powerful “purge” of the surrounding rocks with deep mantle gas with reducing properties and such characteristic elements of kimberlites as europium, cerium, zirconium.

The birth of diamonds not somewhere in unknown “stone caves”, as was previously thought, but in the kimberlite pipes themselves, in the process of their formation, explains the almost perfect preservation of diamond crystals, which are found next to kimberlite pebbles, consisting of rounded, chipped and devoid of edges deep minerals actually extracted from the mantle.

Crystallization of diamonds from gas is also indicated by the constant presence of nitrogen and sometimes boron in them. In the silicate melt of the mantle there is practically no nitrogen or boron, but in the fluid these elements are concentrated because they form gaseous compounds with hydrogen. At some time, radon apparently accumulated in the fluid. It was radon, the strongest alpha emitter, that could create mysterious, unusually beautiful green diamonds. Their color is certainly due to exposure to alpha particles.

Modern industry annually produces millions of tons of soot. It is formed due to the incomplete oxidation of methane. About 80 percent of this soot goes into the production of car tires. A huge amount of soot settles on the walls of countless pipes - stoves, factories, factories, and this does not surprise anyone. But it’s somehow difficult for us to get used to the idea that a diamond is, in essence, also soot, only mantle soot. At first this analogy seems simply blasphemous. So that a too direct analogy of kimberlite pipes with chimneys does not harm the understanding of the natural process, I note that kimberlite pipes never reached the surface of the Earth and did not smoke the sky, like, for example, the pipes of London in the 19th century.

The mantle gas “hung” in the upper layers of the earth’s crust, like a balloon with a gas burner hangs in the air when it has already spent all its energy rising. Therefore, none of the geologists was lucky enough to find a volcano in the middle of the platform, scattering diamond crystals around it. The found kimberlite pipes are opened only by erosion processes. For an explorer, this means that there are many “blind” kimberlite pipes that do not reach the surface. Their presence can be recognized by the detected local magnetic anomalies, the upper edge of which is located at a depth of hundreds, and if you’re lucky, tens of meters. So good luck to you, exploration geologists!

Eagle Stone

There is not even a hint of truth in this legend. Scree diamonds rarely have sharp edges capable of cutting glass. Despite its hardness, diamond is not strong enough to survive a fall from a great height without harm. And most importantly: the legend does not answer the question, where does the eagle get diamonds? After all, not every mountain contains scatterings of precious stones...

Where do diamonds come from?

In an effort to get to the natural deposits of the luminiferous mineral, people have undertaken real excavations more than once or twice in search of diamond veins. However, shoveling soil from diamond-bearing river sediments yielded modest carats per cubic meter of waste rock, and did not help in any way answer the question: where do diamonds come from?

Yellow Diamonds of the Orange River

Soon the field was seething with life. Tens of thousands of amateur miners dug a quarry, reseeded the soil, and handed over the found crystals to buyers. The revival of business activity attracted the attention of the authorities: in 1873, the Earl of Kimberley declared the diamond-bearing lands the property of the British crown, and bestowed his name on the mining village.

Rocks that contained diamonds were called kimberlite, and geological formations that gave the world deposits of sparkling natural stone were called kimberlite pipes.

Glass shaped

Kimberlite, the rock that fills this giant well, consists of varying-scale fragments of locally occurring minerals, unevenly distributed in the highly alkaline environment raised from the deep bowels of the planet.

Olivine, the transparent variety of which is called chrysotile and is a gemstone, is the most voluminous component of kimberlite. Fiery red garnets and layered phlogopites are crystals that are necessarily present in kimberlite massifs.

The kimberlite itself is dark, almost black, and has a pronounced blue or green tint. The crystals of transparent carbon contained in it have a regular diamond-shaped shape and look fresh and new - which sharply contradicts the theories of the genesis of diamonds that were established in the last century...

Where does the kimberlite pipe lead?

Until recently, hypotheses reigned about the formation of a precious mineral at depths from 150 to 600 kilometers. Theoretically, it is there that the temperature and pressure correspond to the parameters of carbon crystallization. However, these theories have little evidence, but their refutations are significant.

Mysteries of kimberlites

Volcanoes “let off steam” where it is easiest for molten rocks to make their way up from the depths: in the transition zones around continental plates, the oceanic crust is both thin (about ten kilometers) and cracked. How does the liquid substance of the mantle manage to break through the most durable layers of the earth's crust and form a kimberlite pipe?

On all continents of the Earth, kimberlite pipes “pierce” - like a nail on a board - the strongest crystalline shields - and often freeze before reaching the surface of several hundred or even tens of meters of loose sedimentary rocks. Why? There is no clear answer.

When talking about kimberlite pipes, geologists use the concept of a volumetric trace of an explosive process. Meanwhile, an explosion - that is, an avalanche-like rapid release of energy - gives completely different consequences. The explosion chamber formed in rocks tends to be spherical - but not a single kimberlite pipe has even a relative similarity to spheroids. This means that the perforation of the earth’s crust during the formation of the kimberlite pipe did not have an explosive nature? How did it go?

It turns out that a kimberlite pipe is a “factory” for the production of diamonds?

Gas needles and hot spots

In approximately the same way, according to Doctor of Geological and Mineralogical Sciences, Professor Alexander Portnov, the formation of a kimberlite pipe occurs. Gas (mainly hydrogen-methane) bubbles collecting in the upper layers of the mantle play the main role in the genesis of kimberlite pipes.

The conditions created in the place where the crystalline continental shield is supported by an accumulation of gas are quite sufficient for the formation of a needle-thin (on a planetary scale) puncture, which makes it possible for mantle gases to rise to the surface of the earth's surface.

The pressure of many tens of thousands of atmospheres inherent in such gas accumulations is capable of destroying and pushing apart stone monoliths - at least in some areas. Perforation does not occur simultaneously: the interaction of compressed superheated gas and the rocks of the continental platform is long-term, and for a successful breakthrough of the hydrogen-methane mixture, a combination of several circumstances is required - otherwise the bubble, having wasted energy, can hang in the depths of the bowels as a slowly cooling gas lens.

In the Earth's lithosphere there are so-called “hot spots” - areas of convective transfer of thermal energy from many hundreds of kilometers of planetary depths to the surface layers. The same processes also occur in a heated liquid - so the presence of a convective thermal “fountain” in the semi-liquid body mass of our planet can be likened to streams of hot water in a boiling kettle.

The difference, however, is that the surface of the water in the kettle is free, and the liquefied substance of the mantle is covered on top with a thick layer of rock “ice”. But the intensity of heat generation at convection points is such that the energy imparted to the solid crust is sufficient to soften it.

Such “springs” of intraplanetary heat flow for several tens of millions of years. And if the relatively thin oceanic crust is melted right through, then the several times thicker continental crust only partially loses its strength under the influence of heat - but does not lose its integrity. Until a gas bubble appears at the place where it is heated...

Gas needle pierces stone

However, closer to the surface, at a depth of several tens or hundreds of meters, the already significantly weakened in strength, but still voluminous and hot gas flow encounters a zone that resembles (in relation to a crystalline monolith of the continental shield) a porous sponge. Without encountering resistance, the mantle gas expands, “blows through” crushed rocks over a vast area around the upper edge of the kimberlite glass - and dissolves in the planet’s atmosphere.

Traces of such interaction are clearly visible. At a distance of up to half a kilometer from a kimberlite pipe, crystalline minerals undergo changes in chemical composition. As a result, they develop (or are greatly enhanced) natural luminescence.

Apatite, which usually glows yellow in ultraviolet light, acquires a blue glow - and this property is characteristic only of apatites found near a kimberlite pipe. Zircon, which rarely exhibits the ability to luminesce, begins to glow clearly and brightly after contact with mantle gases.

And although the colors of gemstones remain unchanged with increased luminescence, the increase in their brightness in daylight and artificial light does not go unnoticed. Jewelry inserts made from such minerals are more expensive.

The ability to re-emit light also increases in other crystalline minerals located near the upper head of the kimberlite pipe. This phenomenon is explained by the chemical activity of mantle gas and the presence in its composition of such metals as europium, zirconium, and cerium. It is they, being introduced into the structure of crystalline formations, that make dull natural stones glow under the rays of the sun.

But where do diamonds come from in kimberlite?

Moreover: on the surface of the stones that underwent a monstrous transfer from the hellish depths to the level of sedimentary rocks, characteristic traces are observed. Heated gas flows melt and deform the surface layers of the crystals, and they become covered with specific folds. This kind of “shagreen” is typical of meteorites and turbine blades.

Diamonds, on the other hand, do not bear any traces of external influence - although moving, for example, along with river pebbles, they roll around, losing their natural rhomboid shape. This means that the perfect shape of diamond crystals confirms the hypothesis about their formation directly in the body of a kimberlite pipe!

But how does it all happen? According to geologists. Meanwhile, in the mantle of the planet, graphite has nowhere to come from and is “forbidden” to be present: at such temperatures and pressures, carbon is unstable and cannot take the form of graphite.

Scientists simply forgot that more than half a century ago, successful experiments were carried out in the Soviet Union on the low-temperature synthesis of diamond from methane. Which simply confirms the possibility of diamond formation in a gaseous fluid rising from the mantle to the surface of the planet.

In the process of decreasing gas pressure as it rises to the surface, conditions arise in the forming kimberlite pipe for the “adjacent” of free valence bonds of a carbon atom to other similar atoms. This is how giant carbon molecules are formed, consisting of countless atoms and which we identify as diamonds.

However, conditions favorable for diamond synthesis do not always arise. This is why only 5-10% of kimberlite pipes contain crystalline carbon.

Additional confirmation of this theory comes from studies of the age of minerals found in kimberlite. The age of that famous pipe near the city of Kimberley is 85 million years. And the garnets (pyropes) found in it were formed more than three billion years ago! The Udachnaya pipe (Yakutia) is 425 million years old. Clinopyroxene, which is part of the Udna kimberlite, is one billion one hundred and forty-nine million years old. However, the age of the Yakut diamonds exactly matches the ages of the “parent” pipes...

There is a lot of other evidence indicating the simultaneous formation of diamonds and kimberlites filling bottomless “wells”. So there is hope for our planet to have a mythical diamond-bearing layer at great depths - at least

Kimberlite pipes from which diamonds are mined are the result of underground volcanic eruptions that occurred millions of years ago. Under the influence of high temperatures and enormous pressure, carbon received a strong crystal lattice and turned into a gemstone. Subsequently, the discovery of this property made it possible to establish the production of artificial diamonds. But natural stones, of course, are much more valuable.

The photo shows a view of the main quarry of the Udachny mining and processing plant - “Udachny”. Mining operations at the deposit of the same name began in 1971, and over the past 25 years the plant has been a leading enterprise in the Russian diamond mining industry and one of the largest open-pit mines in the world. In 2010, the Udachny Mining and Processing Plant accounted for 33.8% of diamond production in value terms and 12.5% ​​of mining operations out of the total volume of the Alrosa group.

The first large-scale industrial diamond mining began in southern Africa about a hundred years ago. In Russia, kimberlite pipes were discovered only in the middle of the last century - in Yakutia. This discovery laid the foundation for Alrosa, today the world leader in diamond mining. Thus, the company’s forecast reserves are about a third of the world’s total, and the explored reserves are sufficient to maintain the current level of production for 25 years without reducing the quality of raw materials. In numbers, the diamond reserves at the deposits owned by Alrosa amount (according to data published in May 2011) to 1.23 billion carats according to the Russian classification (1.014 billion proven and 0.211 billion probable).

For the last five years, the company has annually allocated from 2.5 to 3.5 billion rubles for geological exploration. In 2011, geological exploration costs amounted to about 4 billion rubles, and in 2012 it is planned to allocate over 5.36 billion rubles for these purposes.

At its fields, Alrosa produces about 35 million carats of diamonds per year, being the world's largest producer of this raw material in physical terms: it accounts for about 97% of Russian production and 25% of global production. At the same time, the diamond content in the ore of kimberlite pipes is traditionally low - usually several carats per ton. The Yakut deposits are advantageous in this regard, and are considered one of the richest in content.

In 2010, Alrosa's sales volume of diamonds and rough diamonds amounted to $3.48 billion, and in 2011, according to preliminary data, the company sold $5 billion worth of products - a record figure in its entire history. The company's revenue in the first half of 2011 according to IFRS amounted to 66.15 billion rubles. (+3% compared to the previous year), and net profit increased five times to 26.27 billion.

Kimberlite pipes have the shape of a cone, expanding upward, so their development usually begins with open-pit mining. The design depth of the Udachny quarry, shown in these photographs, is 600 m. To rise from the bottom of the quarry to the surface, the dump truck travels along a serpentine road about 10 km long.

And this is how mining is carried out in quarries. The drilling rig makes a hole into which the explosive is placed (the photo shows the laying process). By the way, although diamond is the hardest mineral, it is quite fragile. Therefore, during blasting operations, gentle technologies are used to preserve the integrity of the crystals as much as possible. After the explosion, the rock fragments are loaded into dump trucks and transported to the processing plant.

The company's main enterprises are located in Western Yakutia, on the territory of four regions of the Republic of Sakha (Yakutia) - Mirninsky, Lensky, Anabarsky, Nyurba - in one of the most severe regions of the planet, with a sharply continental climate, a large temperature difference, in the permafrost zone. In Udachny, winter lasts up to 8 months, the temperature in winter sometimes drops to -60 C. Therefore, most of the equipment is made to order - these are machines adapted to work in low temperature conditions. As a result, work at the fields is carried out all year round in all weather conditions. Quarry work simultaneously involves a large number of equipment - wheel loaders, dump trucks, excavators. There are only about 300 heavy-duty dump trucks in the Alrosa fleet, with a carrying capacity from 40 to 136 tons - mostly BelAZ, there are also Cat and Komatsu.

After reaching a certain depth, reserves within the quarry are exhausted, and open-pit mining becomes unprofitable. On average, quarries are developed to a depth of about 600 m. However, kimberlite pipes lie underground to a depth of 1.5 km. A mine is being built for further development. Underground mining is more expensive than open-pit mining, but it is the only cost-effective way to reach deep-seated reserves. In the future, Alrosa plans to significantly increase the share of underground diamond mining. The company is now completing open-pit mining of the Udachny quarry and, in parallel, is constructing an underground mine. It is expected to launch in 2014.

The cost of switching to underground diamond mining is estimated at $3–4 billion, but in the future this should lead to cost reductions. Largely due to the construction of underground mines, Alrosa’s debt by the acute phase of the crisis in 2008 increased by 64% to 134.4 billion rubles. But the state did not leave the company in trouble: it was included in the list of systemically important enterprises, non-core gas assets were bought by VTB for $620 million, and when the demand for diamonds fell, Gokhran began to buy Alrosa’s products.

When you hear the word “diamond mines,” you involuntarily imagine a beautiful picture: a cave, within the walls of which precious stones shimmer with all the colors of the rainbow. In fact, a diamond mine is not the most romantic place on earth. The walls do not sparkle with a diamond shine, and looking at the ore, it is generally difficult to imagine that the future “best friends of girls” are hidden in it. The photo shows workers in one of the ventilation horizontal openings of the future underground mine, depth - 380 meters.

The construction of mines takes place in unique mining and geological conditions. In addition to permafrost, it is complicated by aggressive groundwater, which, due to high mineralization, can not only erode the walls of mine workings, but also corrode (!) tires of dump trucks. In addition, at Alrosa’s fields there are bitumen and oil shows, which also complicate diamond mining.

In parallel, construction of ground-based facilities of the future mine is underway - for example, ventilation and heating units. The Udachny underground mine will become one of the largest in the world - its productivity is expected to be 4 million tons of ore per year. This is not the company’s first underground mine: since 1999, Alrosa has been working at the Internatsionalny mine. In addition, in August 2009, the company commissioned the Mir underground mine. When all mines reach full capacity, the share of underground mining in Alrosa's total operations is expected to rise to 40%. In total, in Russia the company mines diamonds at 9 primary and 10 alluvial deposits located in Yakutia and the Arkhangelsk region. In addition, the company owns the Catoca diamond mining enterprise in Angola, together with the local state-owned company Endiama.

What will underground mining at Udachny look like in 2-3 years? For example, here is a photograph of the already operating Mir mine. The extraction of diamond ore underground is carried out mainly by combine mining (pictured). The company's specialists are also studying the possibility of using blasthole blasting, traditional for mining - when the rock is destroyed with explosives placed in drilled holes. Then the scheme is the same: loading machines pick up the ore and transport it to the surface, from where it goes to the processing plant. Now we will go there too.

The initial stage of beneficiation of diamond ore looks the same as for any other mineral. Initially, the factory receives large pieces of rock up to several meters in size. After coarse crushing in jaw or cone crushers, the ore is fed to wet autogenous grinding mills (pictured), where rock fragments up to 1.5 m in size are crushed to a size of 0.5 m or less using water.

The controlling stake in Alrosa (51%) is federally owned (from 2006 to 2008, 10% of this stake belonged to VTB), 32% of the shares belong to the government of Yakutia, 8% are controlled by the uluses of this federal subject. In April 2011, the company was transformed from a closed joint stock company to an open joint stock company in order to be able to raise funds on the market. Since the middle of last year, Alrosa shares have been traded on Russian exchanges, but the volume of transactions on them is small due to low liquidity (only shares of minority shareholders were listed on the exchange). In the fall of 2011, Nafta-Moscow of Suleiman Kerimov became a shareholder of Alrosa and bought about 1% of the company’s shares on the market.

At the next stage, spiral classifiers separate the raw materials depending on their density and size. The operating principle is very simple. Water picks up small particles and carries them down the drain. Large particles (up to several centimeters in size) cannot be carried away by water - they settle in the lower part of the tank, after which the spiral lifts them to the top.

Now we need to somehow isolate diamonds from small pieces of ore obtained after crushing. Medium-sized pieces of ore are sent to jigging machines and to heavy-medium concentration: under the influence of water pulsation, diamond crystals are isolated and settle as a heavy fraction. The fine “powder” passes through pneumatic flotation, during which, interacting with reagents, small diamond crystals adhere to the foam bubbles.

At the next stage, all raw materials will go through the main procedure - X-ray luminescent separation (RLS).

It’s just not possible to show what happens inside the separator during its operation: the radar principle is based on constant x-ray radiation. Looking inside while the separator is operating is, to put it mildly, unsafe. If described in words, the method is based on the unique property of diamond - it is the only mineral that luminesces in X-rays. Crushed ore, irradiated with X-rays, constantly moves along the conveyor belt inside the separator. As soon as a diamond enters the irradiation zone, photocells detect the luminescent flash and the air flow “knocks out” the sparkling fragment into a separate tank.

Of course, the air flow inside the separator cannot separate just one small crystal - a certain amount of waste rock is also sifted out along with it. In fact, the entire process of ore beneficiation is aimed only at minimizing the amount of this “empty” material and then facilitating manual processing. Moreover, “manual” in the literal sense of the word: specialists select crystals, clean them and carry out the so-called “final finishing”. No matter how popular the desire to automate all production processes is now, it is absolutely impossible to do without the human factor in diamond mining. The number of employees of the company (as of December 2010) is more than 31,000 people.

But whose hands were these?

One way or another, it was under Fedor Andreev that Alrosa began to prepare for an IPO, and the company was included in the privatization program for 2012–2013. She is currently awaiting a government decision on the parameters and timing of privatization. Representatives of Yakutia stated that the republic sees no obstacles to the privatization of part of the package, but insists that control should remain with the state. Recently, the shareholders agreed that only 14% of shares will be sold on the market (7% each from the Federal Property Management Agency and the Ministry of Property of Yakutia), for which it is planned to earn about $1 billion. Presumably, the placement will take place in the fall of 2012 or spring of 2013 on the MICEX-RTS.

From the final finishing shop, all rough diamonds are sent to the Sorting Center in Mirny. Here, raw materials are divided into main groups and given an initial assessment, after which they can be sent for sale through the Alrosa Unified Sales Organization.

By the way, about half of Alrosa’s products are sold outside of Russia. Until recently, the company sold its diamonds to the world market using the services of the monopolist De Beers. However, at the beginning of 2009, they stopped cooperation and Alrosa began reorganizing its sales system, providing for sales under direct contracts and an equal approach to foreign and Russian buyers, developed its customer base and introduced the practice of “long” contracts.

In general, raw materials from each of the deposits have their own distinctive characteristics. Experienced experts, when looking at a diamond, can determine which mine it came from. But this only applies to general signs. No two diamonds are alike. Therefore, there are no organized exchange trades in diamonds, for example, like gold or copper - this is not a standardized product, each stone has unique characteristics.

This uniqueness significantly complicates both sorting and evaluation. When assessing, experts take three characteristics as a basis: size, color and purity (absence of inclusions inside, transparency). The most expensive stones are “pure water”, absolutely transparent and have no pronounced color. Each of the characteristics has different gradations. As a result, depending on size, color and other parameters, there are about 8,000 possible positions of rough diamonds.

A kimberlite pipe is a vertical or nearly vertical geological body that was formed as a result of a breakthrough through gases. This pillar is truly gigantic in size. The kimberlite pipe has a shape that resembles a huge carrot or glass. Its upper part is a giant conical bulge, but with depth it gradually narrows and finally turns into a vein. In fact, such a geological body is a kind of ancient volcano, the ground part of which was largely destroyed due to erosion processes.

What is kimberlite?

This material is which consists of phlogopite, pyrope, olivine and other minerals. Kimberlite is black in color with greenish and bluish tints. At the moment, more than one and a half thousand bodies of the mentioned material are known, ten percent of which belong to the diamond rock. Experts note that approximately 90% of all diamond reserves are concentrated in kimberlite pipes, and the remaining 10% in lamproite pipes.

Mysteries related to the origin of diamonds

Despite many studies carried out in the field of diamond deposits, modern scientists are still unable to explain some of the features associated with the origin and existence of these precious stones.

Riddle one: why is the kimberlite pipe located exclusively on ancient platforms and shields, which are the most stable and stable blocks of the earth's crust? After all, the thickness of these layers reaches 40 kilometers of rock consisting of basalts, granites, etc. What kind of force is needed to make such a breakthrough?! Why does a kimberlite pipe pierce a powerful platform, and not a thinner one, say, the ocean floor, which is only ten kilometers thick, or transition zones at the boundaries of oceans with continents? After all, in these areas there are hundreds. Geologists are not able to answer this question.

The next mystery is the amazing shape of the kimberlite pipe. In fact, it does not look like a pipe at all, but rather like a huge cone on a thin leg that goes deep into the depths.

The third mystery concerns the unusual shape of the minerals in such rocks. All minerals that crystallize under molten magma conditions form well-cut crystals. Examples include apatite, zircon, olivine, garnet, and ilmenite. They are widespread in kimberlites, but do not have crystalline faces, but resemble. All attempts by geologists to find an answer to this riddle have led nowhere. At the same time, diamonds located next to the mentioned minerals have the ideal shape of octahedrons, which are characterized by sharp edges.

What was the name of the first kimberlite pipe?

The first of these geological bodies that were found and developed by people is located in the south of the African continent in the Kimberley province. The name of this area has become a common noun for all such bodies, as well as for the rock containing diamonds. This first pipe is called the "Big Hole" and is considered the largest quarry developed by humans without the use of machinery. Currently, it has completely exhausted itself and is the main attraction of the city. From 1866 to 1914, the first kimberlite pipe produced 2,722 micrograms of diamonds, amounting to 14.5 million carats. About 50 thousand people worked in the quarry, who used shovels and picks to extract about 22.5 million tons of soil. The development area is 17 hectares, its perimeter is 1.6 km, and its width is 463 m. The depth of the quarry was 240 meters, but after the end of mining it was filled with waste rock. Currently, the “Big Hole” is an artificial lake, the depth of which is only 40 meters.

The largest diamond quarry

Diamond mining in Russia began in the middle of the last century with the discovery in 1954 of the Zarnitsa deposit, which was 32 hectares in size. A year later, a second kimberlite diamond pipe was found in Yakutia, and it was given the name “Mir”. The city of Mirny grew up around this deposit. Today, the mentioned kimberlite pipe (the photo will help the reader imagine the enormity of this diamond deposit) is considered the largest in the world. The depth of the quarry is 525 meters, and the diameter is 1.2 km. Open-pit diamond mining ceased in 2004. Currently, an underground mine is being built to mine the remaining reserves, the extraction of which by open-pit mining is dangerous and unprofitable. According to experts, the development of the tube in question will continue for at least another 30 years.

History of the Mir kimberlite pipe

The development of the field was carried out in harsh climatic conditions. In order to break through the permafrost, it was necessary to blast the rock with dynamite. Already in the 60s of the last century, the deposit produced 2 kg of diamonds per year, and 20 percent of them were of jewelry quality and, after cutting, were supplied to jewelry stores as diamonds. The rest were used for industrial purposes. From 1957 to 2001, the Mir quarry produced diamonds with a total value of $17 billion. During this period, the quarry expanded so much that freight transport had to travel 8 kilometers from the surface to the bottom along a spiral road. Helicopters were strictly forbidden to fly over the object, since the huge funnel simply sucked in all aircraft. The high walls of the quarry are also dangerous for ground transport and people working in mining: there is a risk of landslides. Today, scientists are developing a project for an eco-city, which should be located in a quarry. To do this, it is planned to cover the pit with a translucent dome, on which solar panels will be installed. They plan to divide the space of the future city into tiers: the upper one will be for a residential area, the middle one will be for creating a forest park area, and the lower one will have agricultural purposes.

Conclusion

Diamond mining has a long history. As new deposits were discovered and explored ones were depleted, leadership passed first from India to Brazil, and then to South Africa. At the moment, the leading position is occupied by Botswana, the second place is occupied by Russia.