Diamond occurs in the lower crust of the earth’s crust, at the upper mantle boundary, approximately 150 km below the earth’s surface. It reaches the earth by the movements of the earth’s crust or by volcanic eruptions. With the separation of the continents, the diamonds in the depths approached the earth. This is thought to be the reason why it is common in Africa. Thanks to the technology developed over time, mines can be excavated to reach the diamonds in the upper mantle, and diamonds can be extracted even from under the ocean and even under the glaciers. So how do we find diamonds?
Diamond finder companies utilize a lot of people and machines to find diamonds. There are several places where diamonds can be found. Volcanic rocks, chimneys, alluvial sands, and river coasts are the most important ones. Since diamonds are in the depths of the earth’s crust, it is hard to find them. But with the drilling and exploration studies, they can be found, extracted, and processed to be final products on jewelers’ stands. In this article, I will cover the diamond finding and extracting methods.
Finding Diamonds in Diamond Deposits
The most common theory about the formation of diamonds is that the element carbon crystallized and turned into diamond in this way, millions of years ago, with the greatest temperature and pressure possible only in the very depths of the earth. After its transformations, it erupted to the earth along with other rocks by volcanic action. However, not all diamonds are found in the rocks in which they are formed. They are found in two places: the first in volcanic vents, the second in alluvium.
- Mineral deposits in volcanic vents
The diamond is hidden in a bluish-gray rock called Kimberlite or blue ground. Kimberlite is an iron-rich volcanic rock that turns yellow on earth due to the oxidation of the iron in it. Kimberlite rocks erupt into the earth and form shallow cone-shaped cavities. With the effect of time and erosion, the mouth of the volcanic vent is exposed.
- Alluvial Deposits
Erosive factors such as rainwater, rivers, oceans, and winds constantly drag materials away from their original source and cause them to resediment there. These deposits are called alluvial deposits. Because rivers are constantly changing their sources, the substances carried by the waters may have accumulated in both active river beds and old dried-up river beds. The diamonds found in all alluvial deposits are thought to have come from volcanic vents. Volcano vents are thought to be located upstream of river beds where diamonds are found, but none have been proven.
Due to erosion and loosening of chimneys, diamonds are carried by river water, floods, or rainwater mixed with rivers and accumulate on terraces. Alluvium continues to accumulate because the currents are lighter on the terraces formed by the winding of the rivers. In many regions of the Earth, alluvial deposits have proven to be rich sources of diamonds. Crystals are usually free, not difficult to extract, and rarely need the expensive investments that underground mining entails. Except for volcanic vents, all other diamond deposits are alluvial deposits. Africa’s alluvial diamonds are found in gravel deposits that were once deposited either in river beds or on coastal terraces.
The term “river diamond” is used for fine, colorless diamonds, but in fact, there are diamonds of all colors in the alluvial deposits of South Africa. Some of these alluvial gravels now below the surface were riverbeds that dried up thousands of years ago. For this reason, diamonds coming from the depths of the earth can be found at the top of rock together with materials such as gravel and sand, which were excavated in dry river beds. Diamonds are generally extracted by sieving, washing, straining, and finally classification.
- Coastal Mining
The diamond mines off the southwestern coast of Africa are a unique example of the alluvial sediment variety. Ancient rivers carried diamonds into the sea, hidden in rocks that had ruptured from a kimberlite source. Currents and wave action deposited them along the coast, thus forming sea terraces. For centuries these terraces were covered with layers of sand.
Finding and Extracting Diamonds
Unlike the simple weathering process in alluvial deposits, diamonds extracted from volcanic vents require a very detailed and expensive process. The main vents found in South Africa are Kimberly (no longer functioning), Dutoitspan, De Beer’s, Bultfontein, Wesselton, Jagersfontein and Premier. At first, the ore deposits in the Volcano vents were operated as open pits, but soon the reserves at the mouth filled their capacity and underground mining began thanks to the air pipes.
The main air pipe opens down through the surrounding rocks near the volcanic vent. Tunnels are made horizontally into the main air pipe and expanded vertically from 12 to 25 meters along with the chimney. The blue ground is collapsed by bombing or digging up and away from the air pipe in different layers along the tunnels. Another method is to make cavities. Cone-shaped cavities are dug under the blue pit. Because of the cavities underneath, the Kimberlite rocks lose their balance, the cavities collapse and they fill into cones. Kimberlite is hauled off by mechanical graders transported through tunnels by trucks and brought to the surface.
On the surface, the blue ground is broken up and broken into small pieces, diamonds are separated from kimberlite. The first step is to crush the rocks and pebbles in which the diamonds are hidden. When the blue ground is brought to the factory, it is passed through a coarse sieve to separate material larger than 12 centimeters from the others. Large pieces are transported to the crushing machine by a walking belt. The sieving process continues until the diamonds are separated from the other stones.
Blueground crushing may not seem like a viable way to enrich diamonds, but diamonds are easily separated from the materials they are in this way. It is known that the average size of a rough diamond is less than 30mm in places where large diamonds are enriched outside the Premier mine. It should be noted that in the enrichment process, small stones are more profitable than very large ones. Precautions are taken to avoid breaking large stones. During the crushing process, there is constant supervision when selecting larger stones.
Rotary grinding is a more effective method than crushing in alluvial deposits. The diamond rocks are taken into large pan-shaped containers containing water and pebbles, and by turning them, the rocks are broken and the crystals come out. In another process, the residue is poured with water in large boilers. Washing is usually done with a sieve. Using a sieve of known size, pebbles from crushed rocks are sieved and passed to the bottom.
Diamond Wash Containers
The most important machine used in diamond enrichment is a rotating wash pan, a round vessel that is shoveled and then filled with water. When the machine is started, water and gravel swirl like a swirl, while light materials are thrown away and heavy materials sink to the bottom. The enrichment rate of the diamond extracted from the volcanic vent is 1 in 18 million. E.g; 4 ½ carat diamonds were obtained in an enrichment made from 23 tons of kimberlite rock. Among them, only about one carat is suitable for cutting jewelry.
Moreover, if the diamond is to be cut into a round brilliant shape, it will lose 60% of its weight. Thus, the final weight of the stone after cutting will be 0.40 ct. The enrichment process is different for each sediment. (World average: 300 tons of rock are processed for a one-carat diamond.) In 1897, a De Beers employee discovered that diamonds stick to oil even though other minerals are washed out, and a sloping table was built where the diamonds would get stuck in the oil slick. The oil table was the final processing step before moving on to the manual sorting process.
The separating oil table has been used as a very important diamond enrichment tool until recently. The oil spread on the table is easily scraped off the table, along with the diamonds stuck to it. While many diamonds will adhere to oil, some will not due to the thick layer of salt surrounding the crystals. In this case, preheating is done using a chemical solution, so that the diamonds repel water and adhere to the oil. This process is called annealing.
An optical sorting device is used to inspect the oil table, based on the brilliance, light reflectivity, and light transmission properties of diamonds. Today, color selection is done with optical sorting devices that use photocells to separate diamonds according to their color ratio. A similar device that uses X-rays to assist in the enrichment of diamonds has been produced at the mine. After passing through the oil table, the diamonds are cleaned by boiling and ready for classification and grading.
Modern Methods of Diamond Enrichment
The materials separated in the sieve pass through heavy vehicles in the form of cones. These separator vehicles are cone-shaped tanks, containing sludge with a specific gravity set to 2.6. Ninety-five percent of the ore filled to the brim of the cone has a density less than this mud and therefore floats above the tank. The diamond-containing material with a density greater than 3.2 sinks to the bottom of the cone and is conveyed by an elevator through a pipe. The hydro-cyclone is then made and is more effective than the above method.
To enrich very small diamonds, the concentrates are placed in an abrasive mill and all minerals except the diamond are crushed. Finally, another method used in enrichment is to deliver the concentrate to a high-voltage electrostatic separator plant. The cylinders are connected to the ground on one side and charged on the other. The pebbles are electrically charged and are drawn towards the electrically charged rollers and filled into the conveyor channels. Microscale diamonds are separated from the concentrate by boiling in hydrochloric acid. The diamonds rise above the water and then the diamond surface is scraped off.
While many diamonds glow when exposed to X-rays, nearly all other minerals do not when concentrated with other substances. The concentrate is passed through a machine and when a diamond shines, a photocell causes the door to open. The optical sorter passes the pulp under a beam of light on a tape. It reflects the light detected by a photomultiplier, activating the mechanism that will take the photomultiplier stones to a separate exit point. Since the rest of the pebbles do not shine, they do not activate the photocell.
The diamond search process can be looked at as an example in a wide area. Opening a square-shaped mine to gain access to the diamond-bearing rocks is still a method in use today. To make a logical and accurate estimate of how profitable an area might be, pits are dug and gravel from the pits is filled into boxes, each box with labels showing where the contents were obtained.
Diamond Finder Large Companies
Cecil Rhodes founded De Beers in 1881 at the age of 28. This company he founded enabled him to gain complete control of most of the South African mines by 1887. He began his work by renting a pump to people with prospecting permits. Two more Britons shared this pump. Gradually he bought these official permits and partnered with others. Another person who goes to the diamond fields and has a significant influence on the course of events is Barney Barnoto. Barnato started out as a diamond merchant.
In 1881, he founded the Kimberley Central Mining Company with his brother, after hearing that geoscientists thought there might be a diamond in the blue ground beneath the yellow ground. They took the chance to buy the rights of some prospectors who wanted to give up their exploration rights. Barney Barnato was then twenty-seven years old. This marked the beginning of the race between Rhodes and Barnato for dominance of the great financial empire.
In 1888 the Rhodes and Barney groups merged into a new company, “De Beers United Mines, Ltd.” This company, named South African diamond mine deposits, came under the control of a single company. De Beers company held 90% of the world’s diamond production at that time. However, the discovery of new mines (eg “Premier Mines”) and other alluvial deposits caused De Beers to lose some control of its diamond production. In 1914 it held only 40% of total production.
In 1926, a new name emerged, Ernest Oppenheimer, with the idea to reorganize control of diamond production. He gathered the largest African diamond producers and formed the “Diamond Producers Association” (D.P.A). He also founded the Diamond Trading Company to purchase and classify rough diamonds obtained and produced by D.P.A. Thus, it brought the diamonds to the market with a single sales organization. The name of this organization is “Central Sales Organization” (C.S.O). When Ernest Oppenheimer died on November 25, 1957, he was the director of 41 companies and chairman of 28 companies.
Diamond Resources Where Diamond Can Be Found
In January 1914, the Antwerp press spoke of the first diamonds from Zahira. This first pack contained 6795 carats of diamonds, followed two months later by a second pack containing 500 carats of diamonds. These packages came from Belgium, in less than 25 years Belgium took the lead in diamond production. The former Belgian Congo, today’s Republic of Zaire, is the world’s largest supplier of industrial diamonds with an annual diamond production of 17 million carats, ahead of countries such as South Africa and the U.S.S.R.
World War I dampened interest and curiosity in this discovery. Finally, in 1920, during the first Brussels trade fair, the presence of diamonds in the Congo was officially announced. Congo was given to the Belgian State in 1885 by King Leopold II, who became the monarch. He founded several different companies, including the company “Forminiere” (Societe Internationale Forestiere et Miniere). Diamond exploration in Congo was difficult, and after extensive geological investigation, they decided that the soil was suitable for diamond mining. On May 30, 1907, a nine-person Forminiere delegation led by the American Richard Mohun left the port of Europe.
They reached the city of Leopoldville without any problems, and finally, on July 2 they rowed down the river to Congo and from there to Kasai. They began their research by examining the Kasai streams and Lulua rivers in detail. They even inspected the small teas. As Kasai was about to leave after deciding that it was not a mineral-rich region, a group was formed to conduct a survey in the central direction of Kasai. This group consisted of an experienced Belgian researcher, Narcisse Janot, the famous geoscientist, Millard King Shaler, and the topographer, R. B. Olive.
Shaler and Oliver were American. These three people were accompanied by 150 officers, a dozen workers, and about 90 soldiers. On the evening of November 4, Shaler wrote that while writing about the events that took place that day, Janot was talking about a small, transparent substance, brighter than the one in his hand, which may have formed as a result of diamond crystallization. This little gem was set aside along with other specimens. In late January 1908, this group joined a group tasked with staying there for another year, exploring the rivers and land for another year, before returning to Europe. The small stone Janot found was actually a 0.10-carat diamond.
When they returned to Europe, they forgot about the little apple, although they politely mentioned all the areas they had researched. However, on the evening of November 4, 1907, Shaler, reading his notes, thought that he could find diamonds in the Kasai area. And in 1910, Lanesweert sailed from Europe to Africa with Janot. In August 1911, Janot arrived in Kasai and began searching for minerals. In a few days, he found several diamonds and by September 10, he had more than 240 gems. New discoveries were made: in Tshikapa, then near the Pogge waterfalls, and then in a small river of Tshikapa.
The company’s other prospector found diamonds near the Longatshimo valley. Because of the abundance of discoveries, Forminiere decided to establish the first headquarters in Tshikapa on March 5, 1912. New fields opened. By the end of 1913, about 15,000 carats of diamonds were mined. World War I drastically reduced production in 1914 and 1915. However, agreements with a company were re-arranged and production resumed. 50,000 carats in 1916, 100,000 carats in 1917, and more than 160,000 carats in 1918. Other sites have also been discovered. Especially the Mbuji-Mayi region, which is the richest field discovered to date, has made the Belgian Congo the largest diamond producer in the world.
In 1939, production in the Belgian Congo was equivalent to about 67% of world production. Unfortunately, the vast majority of diamonds mined were of industrial diamond quality. Only 2% were of gem quality. But by 1961, a record production of 18 million carats was realized. This corresponds to 360,000 carats. The diamond extraction methods were pretty much the same as those used in South Africa, and large production will continue for many years to come, thanks to the richness of the region. Average production in 1987 reached 23.35 million carats. This is the second-largest production.
African Diamond Chimneys: Where Diamond Finders Work
In 1870, the first volcanic vent with diamonds was discovered in South Africa. The “Koffiefontein” chimney continued in production for a century, until 1971. In 1893, the “Excelsior” diamond was found in this chimney and weighed 995.20 carats. The “Dutoitspan Mine” was discovered in 1870 near the town of Kimberley. Dry excavation methods were used in the mine. There was no need to use water, as the ground was very sandy and flowed easily through the sieves. The “Dutoitspan”, “Bultfontein”, “De Beers”, “Kimberley”, and “Wesselton” mines are all located near the town of Kimberley and are often referred to as the “De Beers” mines.
In 1903, the mouth of a volcanic vent was explored and was thought to be the largest mine ever discovered. It was called the “Premier Mine”. In 1905, the greatest diamond of all time was found right there. This diamond is called the “Cullinan” diamond, and its weight is 3106 carats. 105 diamonds were cut from this diamond. Later, two more large chimneys were discovered in Africa. These; It is the “Williamson” volcanic vent in Tanzania and the “Orapa” vent in Botswana.
In 1960, Allister T. Fincham found the garnet stone, so he thought he was about to find a volcanic diamond vent. In fact, that’s exactly what he found. Today this chimney is known as the “Finch Mine” and is operated by the “De Beers” company. The largest alluvial deposits are outside the Union of South Africa. It is spread over a very large area covering the territories of Sierra Leone, Zaire, South West Africa, and Angola. The sediments in this region do not look like they will end soon. The great increase in the use of industrial diamonds has increased the importance of the extensive alluvial deposits of Zaire.
In Sierra Leone, methods are used equivalent to those used in operations in volcanic vents. The territory of Sierra Leone harbors gems of very high quality for its industrial enrichment rate. Primitive methods are generally used in alluvial soils, but mechanization is also increasing rapidly. In 1987, South Africa’s average production was 9,053 million carats.
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