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44-564: Murowa consists of three north-trending kimberlite pipes, intrusive into the Chivi suite granites of the Zimbabwe Craton . The kimberlites have been dated at 500 Ma. The Murowa site's possibilities were first realized in 1997 when three diamond-bearing kimberlite pipes were discovered; over a period of three years of study, the two larger pipes have been determined to be economically feasible as mines. Construction of mine facilities

88-581: A diamond rush and led to the excavation of the open-pit mine called the Big Hole . Previously, the term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error. Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes , as well as igneous dykes and can also occur as horizontal sills . Kimberlite pipes are the most important source of mined diamonds today. The consensus on kimberlites

132-438: A maar volcano . Kimberlite dikes and sills can be thin (1–4 meters), while pipes range in diameter from about 75 meters to 1.5 kilometers. Both the location and origin of kimberlitic magmas are subjects of contention. Their extreme enrichment and geochemistry have led to a large amount of speculation about their origin, with models placing their source within the sub-continental lithospheric mantle (SCLM) or even as deep as

176-424: A carrier of diamonds and garnet peridotite mantle xenoliths to the Earth's surface. Its probable derivation from depths greater than any other igneous rock type, and the extreme magma composition that it reflects in terms of low silica content and high levels of incompatible trace-element enrichment, make an understanding of kimberlite petrogenesis important. In this regard, the study of kimberlite has

220-480: A deep mantle origin, where these compounds are more abundant. Kimberlite exploration techniques encompass a multifaceted approach that integrates geological, geochemical, and geophysical methodologies to locate and evaluate potential diamond-bearing deposits. Exploration techniques for kimberlites primarily hinge on the identification and analysis of indicator minerals associated with the presence of kimberlite pipes and their potential diamond cargo. Sediment sampling

264-786: A fine- to medium-grained groundmass. The groundmass mineralogy, which more closely resembles a true composition of the igneous rock, is dominated by carbonate and significant amounts of forsteritic olivine, with lesser amounts of pyrope garnet, Cr- diopside , magnesian ilmenite, and spinel . Olivine lamproites were previously called group II kimberlite or orangeite in response to the mistaken belief that they only occurred in South Africa. Their occurrence and petrology, however, are identical globally and should not be erroneously referred to as kimberlite. Olivine lamproites are ultrapotassic , peralkaline rocks rich in volatiles (dominantly H 2 O). The distinctive characteristic of olivine lamproites

308-460: A large proportion of CO 2 (lower amounts of H 2 O) in the system, which produces a deep explosive boiling stage that causes a significant amount of vertical flaring. Kimberlite classification is based on the recognition of differing rock facies . These differing facies are associated with a particular style of magmatic activity, namely crater, diatreme and hypabyssal rocks. The morphology of kimberlite pipes and their classical carrot shape

352-423: A molar ratio of potassium oxide (K2O) to aluminum oxide (Al2O3) greater than 3, suggesting significant alterations or enrichment processes in their mantle source regions. Characteristic of kimberlites is their abundance in near-primitive elements such as nickel (Ni), chromium (Cr), and cobalt (Co), with concentrations often exceeding 400 ppm for Ni, 1000 ppm for Cr, and 150 ppm for Co. These high levels reflect

396-464: A significant contribution from metasomatized mantle sources, where the rock composition has been altered by fluids. A defining feature of kimberlites is their high volatile content, particularly of water (H2O) and carbon dioxide (CO2). The presence of these volatiles influences the explosivity of kimberlite eruptions and facilitates the transport of diamonds from deep within the mantle to the Earth's surface. The high levels of H2O and CO2 are indicative of

440-461: A trace-mineral assemblage of magnesian ilmenite , chromium pyrope , almandine -pyrope, chromium diopside (in some cases subcalcic), phlogopite , enstatite and of Ti-poor chromite . Group I kimberlites exhibit a distinctive inequigranular texture caused by macrocrystic (0.5–10 mm or 0.020–0.394 in) to megacrystic (10–200 mm or 0.39–7.87 in) phenocrysts of olivine, pyrope, chromian diopside, magnesian ilmenite, and phlogopite, in

484-525: A variety of mineral species with chemical compositions that indicate they formed under high pressure and temperature within the mantle. These minerals, such as chromium diopside (a pyroxene ), chromium spinels, magnesian ilmenite, and pyrope garnets rich in chromium, are generally absent from most other igneous rocks, making them particularly useful as indicators for kimberlites. Kimberlites exhibit unique geochemical characteristics that distinguish them from other igneous rocks, reflecting their origin deep within

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528-795: Is phlogopite macrocrysts and microphenocrysts, together with groundmass micas that vary in composition from phlogopite to "tetraferriphlogopite" (anomalously Al-poor phlogopite requiring Fe to enter the tetrahedral site). Resorbed olivine macrocrysts and euhedral primary crystals of groundmass olivine are common but not essential constituents. Characteristic primary phases in the groundmass include zoned pyroxenes (cores of diopside rimmed by Ti-aegirine), spinel-group minerals (magnesian chromite to titaniferous magnetite ), Sr- and REE -rich perovskite , Sr-rich apatite , REE-rich phosphates ( monazite , daqingshanite), potassian barian hollandite group minerals, Nb-bearing rutile and Mn-bearing ilmenite . Kimberlites are peculiar igneous rocks because they contain

572-790: Is a fundamental approach, where kimberlite indicator minerals (KIMs) are dispersed across landscapes due to geological processes like uplift, erosion, and glaciations. Loaming and alluvial sampling are utilized in different terrains to recover KIMs from soils and stream deposits, respectively. Understanding paleodrainage patterns and geological cover layers aids in tracing KIMs back to their source kimberlite pipes. In glaciated regions, techniques such as esker sampling, till sampling, and alluvial sampling are employed to recover KIMs buried beneath thick glacial deposits. Once collected, heavy minerals are separated and sorted by hand to identify these indicators. Chemical analysis confirms their identity and categorizes them. Techniques like thermobarometry help understand

616-467: Is challenging due to significant overburden or weathering. These methods leverage physical property contrasts between kimberlite bodies and their surrounding host rocks, enabling the detection of subtle anomalies indicative of potential kimberlite deposits. Airborne and ground surveys, including magnetics, electromagnetics, and gravity surveys, are commonly employed to acquire geophysical data over large areas efficiently. Magnetic surveys detect variations in

660-505: Is that they are formed deep within the mantle . Formation occurs at depths between 150 and 450 kilometres (93 and 280 mi), potentially from anomalously enriched exotic mantle compositions, and they are erupted rapidly and violently, often with considerable carbon dioxide and other volatile components. It is this depth of melting and generation that makes kimberlites prone to hosting diamond xenocrysts . Despite its relative rarity, kimberlite has attracted attention because it serves as

704-468: Is the result of explosive diatreme volcanism from very deep mantle -derived sources. These volcanic explosions produce vertical columns of rock that rise from deep magma reservoirs. The eruptions forming these pipes fracture the surrounding rock as it explodes, bringing up unaltered xenoliths of peridotite to surface. These xenoliths provide valuable information to geologists about mantle conditions and composition. The morphology of kimberlite pipes

748-405: Is varied, but includes a sheeted dyke complex of tabular, vertically dipping feeder dykes in the root of the pipe, which extends down to the mantle. Within 1.5–2 km (0.93–1.24 mi) of the surface, the highly pressured magma explodes upwards and expands to form a conical to cylindrical diatreme , which erupts to the surface. The surface expression is rarely preserved but is usually similar to

792-568: The 1870s in Kimberley sparked a diamond rush , transforming the area into one of the world’s largest diamond-producing regions. Since then, the association between kimberlites and diamonds has been crucial in the search for new diamond deposits around the globe. Kimberlites also serve as a window into the Earth's past, offering clues about the formation of continents and the dynamic processes that shape our planet. Their distribution and age can provide insights into ancient continental movements and

836-463: The 3D model serves as a valuable decision-making tool, offering insights into potential diamond-bearing potential, identifying high-priority drilling targets, and guiding exploration strategies to maximize the chances of successful diamond discoveries. Kimberlites are a valuable source of information about the composition of the Earth's mantle and the dynamic processes that occur within it. The study of kimberlites has contributed to our understanding of

880-401: The Earth is rich in magnesium . They are well known as the primary source of diamonds , and are mined for this purpose. Volcanic pipes are relatively rare by this definition based on minerals and depth of the magma source, but on the other hand volcanic diatremes are common, indeed the second commonest form of volcanic extrusion (that is magma that reaches the surface). Volcanic pipes form as

924-423: The Earth's deep interior, including its physical conditions, composition, and the evolutionary history of the planet. The role of kimberlites in diamond exploration cannot be overstated. Diamonds are formed under the high-pressure, high-temperature conditions of the Earth's mantle. Kimberlites act as carriers for these diamonds, transporting them to the Earth's surface. The discovery of diamond-bearing kimberlites in

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968-598: The Earth's magnetic field caused by magnetic minerals within kimberlites, which typically exhibit distinct magnetic signatures compared to surrounding rocks. Electromagnetic surveys measure variations in electrical conductivity, with conductive kimberlite bodies producing anomalous responses. Gravity surveys detect variations in gravitational attraction caused by differences in density between kimberlite and surrounding rocks. By analyzing and interpreting these geophysical anomalies, geologists can delineate potential kimberlite targets for further investigation, such as drilling. However,

1012-484: The Earth's mantle. These features provide insights into the mantle's composition and the processes involved in the formation and eruption of kimberlite magmas. Kimberlites are classified as ultramafic rocks due to their high magnesium oxide (MgO) content, which typically exceeds 12%, and often surpasses 15%. This high MgO concentration indicates a mantle-derived origin, rich in olivine and other magnesium-dominant minerals. Additionally, kimberlites are ultrapotassic, with

1056-518: The Earth’s deep geochemical cycles and the mechanism of mantle plumes , which are upwellings of abnormally hot rock within the Earth's mantle. Moreover, kimberlites are unique in their ability to transport material from the Earth's mantle to its surface. This process, known as xenolith transport, provides geologists with samples of the Earth's mantle, which are otherwise inaccessible. Analyzing these samples has led to significant advances in our knowledge of

1100-474: The assembly and breakup of supercontinents . Kimberlites are the most important source of primary diamonds . Many kimberlite pipes also produce rich alluvial or eluvial diamond placer deposits . About 6,400 kimberlite pipes have been discovered in the world, of those about 900 have been classified as diamondiferous, and of those just over 30 have been economic enough to diamond mine. The discovery of diamond-rich kimberlite pipes in northern Canada during

1144-424: The collection and integration of various datasets, including drill-hole data, ground geophysical surveys, and geological mapping information. These datasets are then integrated into a cohesive digital platform, often utilizing specialized software packages tailored for geological modeling. Through advanced visualization techniques, geologists can create detailed 3D representations of the subsurface geology, highlighting

1188-415: The conditions under which these minerals formed and where they came from in the Earth's mantle. By analyzing these indicators and geological curves, scientists can estimate the likelihood of finding diamonds in a kimberlite pipe. These methods help prioritize where to drill in the search for valuable diamond deposits. Geophysical methods are particularly useful in areas where direct detection of kimberlites

1232-479: The diamonds. See also Mir Mine and Udachnaya pipe , both in the Sakha Republic , Siberia . The blue and yellow ground were both prolific producers of diamonds. After the yellow ground had been exhausted, miners in the late 19th century accidentally cut into the blue ground and found gem-quality diamonds in quantity. The economic situation at the time was such that, with a flood of diamonds being found,

1276-432: The distribution and geometry of kimberlite bodies alongside other significant geological features such as faults, fractures, and lithological boundaries. Within the model, efforts are made to accurately depict the internal phases of kimberlite pipes, incorporating different facies , country rock xenoliths, and mantle xenoliths identified through careful interpretation of drill-core data and geophysical surveys. Once validated,

1320-416: The early 1990s serves as a prime example of how challenging these deposits can be to locate, as their surface features are often subtle. In this case, the pipes were hidden beneath ice-covered shallow ponds, which filled depressions formed by the softer kimberlite rock eroding slightly faster than the surrounding harder rock. The deposits occurring at Kimberley , South Africa , were the first recognized and

1364-525: The interpretation of geophysical data requires careful consideration of geological context and potential masking effects from surrounding geology, highlighting the importance of integrating geophysical results with other exploration techniques for accurate targeting and successful diamond discoveries. Three-dimensional (3D) modeling offers a comprehensive framework for understanding the internal structure and distribution of key geological features within potential diamond-bearing deposits. This process begins with

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1408-628: The isotopic affinities of these rocks using the Nd , Sr , and Pb systems. Roger Mitchell later proposed that these group I and II kimberlites display such distinct differences, that they may not be as closely related as once thought. He showed that group II kimberlites show closer affinities to lamproites than they do to group I kimberlites. Hence, he reclassified group II kimberlites as orangeites to prevent confusion. Group-I kimberlites are of CO 2 -rich ultramafic potassic igneous rocks dominated by primary forsteritic olivine and carbonate minerals, with

1452-431: The magma act corrosively on the overlying rock, resulting in a broader cone of eviscerated rock (the ejection of this rock also forms a tuff ring, like kimberlite eruptions). This broad cone is then filled with volcanic ash and materials. Finally, the degassed magma is pushed upward, filling the cone. The result is a funnel shaped deposit of volcanic material (both solidified magma, and ejecta) which appears mostly flat from

1496-406: The magma upward at rapid speeds, resulting in a supersonic Plinian eruption . In kimberlite pipes, the eruption ejects a column of overlying material directly over the magma column, and does not form a large above-ground elevation as typical volcanoes do; instead, a low ring of ejecta known as a tuff ring forms around a bowl-shaped depression over the subterranean column of magma. Over time,

1540-515: The miners undercut each other's prices and eventually decreased the diamonds' value down to cost in a short time. Volcanic rocks : Subvolcanic rocks : Plutonic rocks : Picrite basalt Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Microdiorite Diorite Dacite Microgranodiorite Granodiorite Rhyolite Microgranite Granite Volcanic pipe Volcanic pipes or volcanic conduits are subterranean geological structures formed by

1584-444: The potential to provide information about the composition of the deep mantle and melting processes occurring at or near the interface between the cratonic continental lithosphere and the underlying convecting asthenospheric mantle. Many kimberlite structures are emplaced as carrot-shaped, vertical intrusions termed " pipes ". This classic carrot shape is formed due to a complex intrusive process of kimberlitic magma, which inherits

1628-546: The previous owner of the mine, Harpal Randhawa, died alongside his son and 4 other passengers in a plane crash. Kimberlite Kimberlite , an igneous rock and a rare variant of peridotite , is most commonly known to be the main host matrix for diamonds . It is named after the town of Kimberley in South Africa , where the discovery of an 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned

1672-463: The primitive nature of their mantle source, having undergone minimal differentiation. Kimberlites show enrichment in rare earth elements (REEs), which are pivotal for understanding their genesis and evolution. This enrichment in REEs, along with a moderate to high large-ion lithophile element (LILE) enrichment (ΣLILE > 1,000 ppm), including elements like potassium , barium, and strontium, points to

1716-460: The result of violent eruptions of deep-origin volcanoes. These volcanoes originate at least three times as deep as most other volcanoes, and the resulting magma that is pushed toward the surface is high in magnesium and volatile compounds such as water and carbon dioxide . As the body of magma rises toward the surface, the volatile compounds transform to gaseous phase as pressure is reduced with decreasing depth. This sudden expansion propels

1760-452: The source of the name. The Kimberley diamonds were originally found in weathered kimberlite, which was colored yellow by limonite , and so was called "yellow ground". Deeper workings encountered less altered rock, serpentinized kimberlite, which miners call "blue ground". Yellow ground kimberlite is easy to break apart and was the first source of diamonds to be mined. Blue ground kimberlite needs to be run through rock crushers to extract

1804-461: The transition zone. The mechanism of enrichment has also been the topic of interest with models including partial melting, assimilation of subducted sediment or derivation from a primary magma source. Historically, kimberlites have been classified into two distinct varieties, termed "basaltic" and "micaceous" based primarily on petrographic observations. This was later revised by C. B. Smith, who renamed these divisions "group I" and "group II" based on

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1848-436: The tuff ring may erode back into the bowl, leveling out the depression by filling it with washed-back ejecta. Kimberlite pipes are the source of most of the world's commercial diamond production, and also contain other precious gemstones and semi-precious stones, such as garnets , spinels , and peridot . Lamproite pipes operate similarly to kimberlite pipes, except that the boiling water and volatile compounds contained in

1892-401: The violent, supersonic eruption of deep-origin volcanoes . They are considered to be a type of diatreme . Volcanic pipes are composed of a deep, narrow cone of solidified magma (described as "carrot-shaped"), and are usually largely composed of one of two characteristic rock types — kimberlite or lamproite . These rocks reflect the composition of the volcanoes' deep magma sources, where

1936-478: Was completed in late 2004. Preparation for mining included the forced relocation of 926 people living on the mine site to six farms purchased by a government relocation program. Limited mining operations began in Murowa in 2004, with full capacity expected to be reached sometime in 2005, although permitting problems slowed progress towards this milestone. In 2018, 1,018,776 tonnes of diamonds were processed. In 2023,

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