Ass #4 - Diamond Exploration & Mining PDF

ASS #4 : Diamond Exploration & Mining Deposits: - Deposits of diamonds found in the kimberlite or lamproite that brought them to the surface are known as primary deposits. Secondary Deposit: -Diamonds are also found outside their pipes, in secondary deposits, Diamonds are also found outside their...

ASS #4 : Diamond Exploration & Mining Deposits: - Deposits of diamonds found in the kimberlite or lamproite that brought them to the surface are known as primary deposits. Secondary Deposit: -Diamonds are also found outside their pipes, in secondary deposits, Diamonds are also found outside their pipes, in secondary deposits, -when diamonds are caught in small whirlpools in river and being heavy they sink to the bottom forming alluvial deposits -If the river currents are strong enough, they might carry diamonds all the way to the sea. There, ocean currents deposit them offshore or wash them back onto the beach and are considered marine deposits -Secondary deposits are usually much richer in diamonds than primary deposits. This is because the host rock and lighter rock materials erode and wash away, leaving concentrations of diamonds and heavier minerals,The water’s rolling and tumbling action breaks down most of the heavily included diamonds, so only higher-quality crystals remain intact in these marine deposits Diamond Exploration: -The entire process, from beginning a search to mining the first diamonds, usually takes more than 10 years -Diamondiferous (diamond-bearing) deposits occupy an extremely small percentage of the earth’s crust, -Clifford's Rule,The rule states that although not all kimberlites contain diamonds, those that do occur only on these very old cratons on top of deep mantle keels, kimberlite eruptions originate below cratons. Therefore, most diamond-bearing kimberlites tend to be found on cratons, however discoveries in Australia prove geologists now consider not only cratons when looking for new diamond deposits, but also the areas around cratons. -Scientists once searched for these areas using sound waves to develop images of underground rock layers and structure, A craton is denser than the younger surrounding rock, so when a sound wave strikes it, the wave moves faster. -Secondary deposits are found when geologist look for ancient or current streams, rivers, and estuaries (tidal mouths of rivers) flowing away from cratons, or those that are located on direct paths from or near known kimberlite or lamproite pipes,Modern exploration for alluvial deposits uses several methods, including aerial photography, satellite imaging, and radar, to detect potential alluvial sites. -Field mapping and soil sampling are more traditional methods. Narrowing the Search: - Gravity surveys to measure density variations in the ground to detect kimberlite or lamproite - Magnetic and electromagnetic surveys are also widely used in diamond exploration. Both survey methods send energy waves to the surface of the earth and collect the waves that bounce off to determine the features of the underground rocks. - Magnetic surveys plot variations in magnetic response, and kimberlite’s is distinct - Seismic surveys work similarly to magnetic and electromagnetic surveys but use sound waves to detect the features of different rocks. Locating Deposits: - when indicator minerals are found then a pipe isn't to far away, mineral samples are then taken,Common indicator minerals found in association with kimberlite and lamproite include red and orange garnet, black spinel, diopside, olivine, ilmenite, chromite, and perovskite. - when indicator minerals aren't found geochemical testing is used to determine a sample’s chemical composition. Samples of rocks, soil, or even vegetation in the targeted area are tested for certain elements that are present in indicator minerals. Testing Deposit Viability: - larger samples need to be extracted to determine if the project is continued or abandoned, at this stage 3 levels of samples are taken - first is microdiamond testing, which looks for tiny diamonds in a sample gathered from drilling cores from primary deposits or from river gravels or seafloor sediments in secondary deposits. - if the first level of testing is promising the next step is Character Sampling which gives a general idea of diamond size, shape, clarity, and color based on processing up to 500 tons of earth determining ore grade - The ore grade: the concentration of diamonds measured by the amount of diamonds in 100 tons of rock. - Last a Bulk Sample where between 5,000 and 10,000 tons of earth are processed during bulk sampling, A parcel of about 2,000 carats of diamonds needs to be produced for an accurate evaluation, - secondary deposits require a larger bulk sample (parcel of 3,000 to 5,000 carats is typically required) then a pipe do to them being shallow and wide Primary Deposit: - The basic approach to mining a primary deposit is to dig out and remove all the material in and around the pipe at a kimberlite or lamproite deposit Open Pit Mining: - open-pit mine usually begins with the removal of layers of overburden—rock or soil—that cover the pipe, it is removed and processed for any diamonds it might contain, Due to its yellowish color, it is called yellow ground. - the hard rock below the overburden often has a bluish color and is called blue ground. - insert explosives into the holes, and blast the ore loose. Low-velocity charges are used to avoid shattering the diamonds open-pit mine is developed, it forms a deepening cone that follows the contours of the diamond pipe, As the pit deepens, the quantity of diamonds decreases and it becomes much narrower and more difficult for the giant trucks to move in Under Ground Mine: - An underground mine consists of a series of vertical shafts and horizontal tunnels in and around a pipe. - horizontal tunnels called drifts are drilled from the shafts through the pipe to extract the ore. - Cave Mining is the most common underground diamond mining method, the orebody is drilled beneath the surface and recovered as it falls and removal of the orebody leaves a large “cave” where it once was then concrete-lined tunnels are built directly under a large section of ore Diamond Recovery: - Sizing Step- the fairly large chunks of ore are reduced so they are easier to manage -reduce ore size to a couple of inches Concentration: -Dense Media Separation: The process of separating the diamond-bearing ore from the lighter waste materials (also known as heavy media separation) -crushed and scrubbed ore is mixed with a heavy liquid and fed into cyclone that spins the mixture, forcing the liquid and diamond-bearing material downward with a centrifugal force,dryers then evaporate the liquid, leaving the solid material Recovery: -Grease belt and X-ray separation are both common methods, Diamond has an affinity for grease and oils, so it sticks to the grease on the belt, and the remaining minerals are washed away by the water that flows constantly over its surface -X-ray separation process for recovering diamonds. This process is based on the fact that diamonds almost always fluoresce (emit visible light) when exposed to X-rays Mining Secondary Deposit : - Alluvial Mining : - today accounts for only about 15 percent of diamond production and many contain only a small percentage of diamonds., the shift from secondary to primary deposits was due primarily to the improved technologies used to locate and mine primary deposits. - its' not economical for larger mining companies to mine these areas, however it can be for individual miners - earlier artisanal miners adopted techniques from gold miners - large-scale alluvial mining is rare, but operations, recovery and sieving are mechanized, Lulo mine is a large alluvial diamond mine with a mining lease of over 3,000 square km and is only 150 km from one of the largest diamond mines in the world, Catoca Marine Mining: - a variety of methods for marine mining. These include modified alluvial mining (large-scale mechanized mining); shallow-water mining using divers; and deep-sea operations involving sophisticated, high-tech ships and vessels - first method is onshore mining. The pounding action of the surf can force diamonds into small cracks and crevices in the seabed and shoreline. Dislodging and removing these diamonds often requires special tools and procedures. - Namibian onshore mining is one of the world’s largest earthmoving operations - Offshore deposits are divided into two zones based on the depth of the water. Deposits in water less than 15 m deep can be mined by divers, Divers in shallow-water mining operations use a hose attached to a suction pump located on shore or in a boat. The diver vacuums gravel off the ocean floor which is sieved later Deep Diving: - Mining companies use sophisticated equipment like sonar, along with data from global positioning satellites, to develop remarkably accurate maps of the undersea floor identifying diamond deposits, such as ravines, basins, and ridges - Divers in special heated diving suits go down to depths of about 40 m, also the use automated crawlers equipped with devices that vacuum material from the ocean floor - crawlers target area and begins to dredge. The dredged sediments are pumped up to the ship via a giant pipe Mining Economics: - mining companies evaluate these factors: - Deposit size - Large pipes are likely to contain more diamonds than small pipes. Rough diamond concentration,- measured by ore grade. Rough diamond size and quality. Major Diamond Sources : -The largest producers by value (U.S. dollars) and by volume (carats) include Russia, Botswana, and Canada. Africa: -Africa has been the most important diamond-producing area for nearly a century and a half, since the first diamond discovery there in the late 1800s and has the world’s most diverse diamond sources. -Botswana is one of the top three diamond-producing countries by value and volume. -Orapa is Debswana’s oldest mine and Botswana’s largest,Jwaneng, the world’s richest diamond mine in terms of value -Venetia, run by De Beers, and Petra’s Finsch are well established and produce millions of carats of rough yearly and Cullinan is famous for its blue diamonds, the world’s largest rough diamond, and many important stones in the British Crown Jewels. Australia: -three diamond mines on this continent: Argyle, Ellendale, and Merlin. Argyle, the nation’s flagship diamond mine, was the most economically important. Until its closure beginning in 2020, Argyle was the major supplier of colored diamonds, especially pink, violet, and brown stones. -Prior to this it was a major diamond supplier to the global market in terms of volume. The closure caused Australia’s diamond production to drop by 99 percent. The Americas: -Both the United States and Canada have diamond deposits. -Many consider Canada one of the top three largest diamond-producing countries in terms of both value and volume. -Deposits in the U.S. do not have much economic significance. Canada: -Northwest Territories: One pipe was developed into the first diamond mine in the nation: Ekati. This mine now has both open-pit and underground operations. In 2003 the Diavik mine began to produce diamonds. In 2017 Renard and Gahcho Kué began production, which pushed Canada’s diamond production higher. United States: -Murfreesboro, Arkansas. Four pipes were discovered in the area, two of which have produced diamonds. However, the yield from the pipe was found to be mainly industrial grade and of low profit. Brazil: -Many operations are concentrated in Brazil’s Mato Grosso and Minas Gerais states. Most mining is of alluvial deposits, although small kimberlites have been found. Prior to the discoveries in Africa, Brazil was the top diamond producer after India. Eurasia: -India was the only diamond source for centuries. Diamonds have been found at a couple locations in China as well. But the most important producer today is Russia. Russia: -Russia is a major diamond producer by volume, providing about a third of the world’s supply in carats. -The majority of Russia’s diamond mines are operated by ALROSA -These mines use state-of-the-art technologies. Mir, Jubilee, and Udachny are some of the most famous Russian mines, 11 kimberlite pipes and 16 alluvial deposits are being mined, many in areas of extremely harsh climate. -Lomonosov has the potential to be the next important source of colored diamonds. Pink, yellow, green, and brown diamonds are all found here,especially pink and purple which are always in high demand