The deposits of diamonds are divided into alluvial and indigenous, among which types and subtypes are distinguished, differing in terms of occurrence, the shape of ore bodies, concentrations, quality and stocks of diamonds, extraction and enrichment conditions.
Indigenous deposits of kimberlite-type diamonds are the main objects of operation throughout the world. Of these, about 80% of natural diamonds are mined. According to diamond stocks and sizes, they are divided into unique, large, medium and small. With the highest profitability, the upper horizons of the unique and large deposits emerging on the day surface are worked out. They contain the main reserves and forecasted diamond resources of individual diamondiferous kimberlite fields. Kimberlites are “volcanic vents” filled with breccias. Breccia consists of debris and xenoliths surrounding and deposited from above rocks, from debris of rocks taken from depths of 45-90 km and more.
The cement is a volcanic material, tuffs of alkaline-ultra-basic composition, the so-called kimberlites and lamproites. Kimberlite pipes are located on platforms, lamproite – in their folded frame. The time for the formation of tubes varies from Archaean to Cenozoic, and the age of diamonds, even the youngest, is about 2-3 billion years. The formation of the tubes is associated with a breakthrough upward through narrow channels at a high pressure, at a depth of more than 80 km, at a temperature of about 1000 alkaline-ultrabasic melts. Most of the well-studied kimberlite bodies have a complex structure; In the most simplified case, the structure of the tube involves two main varieties of rocks formed during two consecutive phases of introduction: breccia (1st stage) and massive “large-porphyry” kimberlite (2nd stage). In the structure of some kimberlite pipes, kimberlite dikes and veins associated with tubes were also identified. Blind bodies, formed by portions of kimberlite magma, did not reach the surface of the day. Deposits associated with dikes and veins of kimberlites are usually classified as small, less often average in diamond reserves. In many cases, a breakthrough has reached the paleo-surface, but many explosion tubes can be “blind” and have not yet been eroded by erosion .e. Lie somewhere in the depths. But even on the surface of the Earth there are places where there are enough pressures to form a diamond. These are the places of impact of meteorites, where the diamond is found not only in the Earth, but also in a number of meteorites themselves.
The velocity of the breakthrough magma probably could be very large, about 800 km / h, magma tore and carried up fragments of different composition. If they contained diamonds, the tube became diamond-bearing. Diamonds themselves are the most stable polymorphic modification of carbon in the deep zones of the Earth.
Lamproite type of diamond deposits was discovered relatively recently (1976) in Western Australia, where a large Argyll deposit is being exploited. In their structure, lamproite deposits are generally similar to kimberlite deposits. Judging by the Argyll exploration data, lamproite tubes somewhat wedge to a depth where they pass into dikes. The system of mining of these deposits and the technology of enrichment are the same as those at kimberlite objects.
Kimberlite-lamproite type is represented by a diamond deposit in the Arkhangelsk region, where the content of indicator minerals is significantly lower than in “classical” kimberlites, the overwhelming majority of diamonds are represented by the curved forms.
Ring impact structures ranging in size from the first to hundreds of kilometers are associated with super-powerful explosive processes, the source of which, according to different researchers, was either extraterrestrial (the fall of large celestial bodies) or endogenous in nature. In Russia, one deposit of this type was discovered – Popigajskoe on the eastern slope of the Anabar crystalline massif. In terms of ore reserves and the content of diamonds, the deposit exceeds hundreds of times the largest in kimberlites. However, diamonds in impact fields are encased in strong dense effusive rocks and are represented exclusively by technical varieties with admixture of lonsdaleite (a polymorphic modification of carbon, found in the form of plates alternating with graphite, but located perpendicular to its plane).
The metamorphogenic type is also represented by one deposit in Kazakhstan, where diamonds are found in biotite gneisses, biotite-quartz, garnet-pyroxene and pyroxene-carbonate rocks. According to the reserves and the content of diamonds, it is ten times higher than the largest high-diamond-bearing kimberlite pipes. Diamonds have an extremely small crystal size, and jewelry and high-quality technical varieties have not yet been found.