Kimberlite

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Kimberlite
Igneous rock
Kimberlite picture.jpg
Kimberlite from the United States
Composition
Forsteritic olivine and carbonate minerals, with trace amounts of magnesian ilmenite, chromium pyrope, almandine-pyrope, chromium diopside, phlogopite, enstatite and titanium-poor chromite. Sometimes contains diamonds.
False-color scanning electron microscope image of kimberlite from South Africa. Olivine crystals (green) are in a fine-grained matrix made up of clay minerals and carbonates (presented in blue, purple and buff colors). Kimberlite crosssection QEMSCAN.png
False-color scanning electron microscope image of kimberlite from South Africa. Olivine crystals (green) are in a fine-grained matrix made up of clay minerals and carbonates (presented in blue, purple and buff colors).

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 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.

Contents

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 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 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 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.

Morphology and volcanology

Distribution of kimberlites in Africa. Cratons: CA-Central African (Kasai), SA-South African (Kalahari), WA-West African; Kimberlites (shown as red dots): B-Banankoro, Cu-Cuango Valley, Do-Dokolwayo, F-Finsch, G-Gope, J-Kwaneng, Ja-Jagersfontein, k-Koidu, Kb-Kimberley, Ko-Koffiefontein, L-Letlhakane, Le-Letseng, Lu-Lunda, M-Mitzic, Mb-Mbuji-Mayi, Mw-Mwadui, O-Orapa, P-Premier, R-River Ranch, V-Venetia. Kimberlite Pipes in Africa.png
Distribution of kimberlites in Africa. Cratons: CA-Central African (Kasai), SA-South African (Kalahari), WA-West African; Kimberlites (shown as red dots): B-Banankoro, Cu-Cuango Valley, Do-Dokolwayo, F-Finsch, G-Gope, J-Kwaneng, Ja-Jagersfontein, k-Koidu, Kb-Kimberley, Ko-Koffiefontein, L-Letlhakane, Le-Letseng, Lu-Lunda, M-Mitzic, Mb-Mbuji-Mayi, Mw-Mwadui, O-Orapa, P-Premier, R-River Ranch, V-Venetia.

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 a large proportion of CO2 (lower amounts of H2O) in the system, which produces a deep explosive boiling stage that causes a significant amount of vertical flaring. [1] 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. [2] [3]

The morphology of kimberlite pipes and their classical carrot shape 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. [4] [5] The morphology of kimberlite pipes 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 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. [6]

Petrology

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 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. [7] This was later revised by C. B. Smith, who renamed these divisions "group I" and "group II" based on the isotopic affinities of these rocks using the Nd, Sr, and Pb systems. [8] 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. [9]

Group I kimberlites

Group-I kimberlites are of CO2-rich ultramafic potassic igneous rocks dominated by primary forsteritic olivine and carbonate minerals, with 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 a fine- to medium-grained groundmass. [10]

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

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. [11] Olivine lamproites are ultrapotassic, peralkaline rocks rich in volatiles (dominantly H2O). The distinctive characteristic of olivine lamproites 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.

Kimberlitic indicator minerals

Kimberlites are peculiar igneous rocks because they contain 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.

Geochemistry

Kimberlites exhibit unique geochemical characteristics that distinguish them from other igneous rocks, reflecting their origin deep within 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.

Composition

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 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.

Elemental Abundance

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 the primitive nature of their mantle source, having undergone minimal differentiation.

Rare Earth and Lithophile Elements

Kimberlites show enrichment in rare earth elements (REEs), [12] which are pivotal for understanding their genesis and evolution. This enrichment in REEs, along with a moderate to high large-ion lithophile element (LILE) [13] enrichment (ΣLILE > 1,000 ppm), including elements like potassium, barium, and strontium, points to a significant contribution from metasomatized mantle sources, where the rock composition has been altered by fluids.

Volatile Content

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 a deep mantle origin, where these compounds are more abundant. [14]

Exploration techniques

Kimberlite exploration techniques encompass a multifaceted approach that integrates geological, geochemical, and geophysical methodologies to locate and evaluate potential diamond-bearing deposits. [15]

Indicator minerals sampling

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 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 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. [16] [17]

Geophysical methods

Geophysical methods are particularly useful in areas where direct detection of kimberlites 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 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, 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. [15] [18]

3-D modeling

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 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 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, 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. [19] [20]

Historical significance

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 the Earth’s deep geochemical cycles and the mechanism of mantle plumes, which are upwellings of abnormally hot rock within the Earth's mantle. [21]

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 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 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. [22] [23]

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 the assembly and breakup of supercontinents. [24]

Economic importance

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. [25] [26]

The deposits occurring at Kimberley, South Africa, were the first recognized and 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 the diamonds. [27]

Mir mine Mirny in Yakutia.jpg
Mir mine

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, the miners undercut each other's prices and eventually decreased the diamonds' value down to cost in a short time. [28]

Related Research Articles

<span class="mw-page-title-main">Magma</span> Hot semifluid material found beneath the surface of Earth

Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles.

<span class="mw-page-title-main">Xenolith</span> Rock inside a rock with a different composition

A xenolith is a rock fragment that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations, even in areas which are spatially limited, e.g. rhyolite-dominated lava of Niijima volcano (Japan) contains two types of gabbroic xenoliths which are of different origin - they were formed in different temperature and pressure conditions.

<span class="mw-page-title-main">Peridotite</span> Coarse-grained ultramafic igneous rock type

Peridotite ( PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

<span class="mw-page-title-main">Phlogopite</span> Member of the mica family of phyllosilicates

Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica.

<span class="mw-page-title-main">Diopside</span> Pyroxene mineral

Diopside is a monoclinic pyroxene mineral with composition MgCaSi
2O
6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.

<span class="mw-page-title-main">Eclogite</span> A dense metamorphic rock formed under high pressure

Eclogite is a metamorphic rock containing garnet (almandine-pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum and, rarely, diamond. The chemistry of primary and accessory minerals is used to classify three types of eclogite. The broad range of eclogitic compositions has led to a longstanding debate on the origin of eclogite xenoliths as subducted, altered oceanic crust.

<span class="mw-page-title-main">Pyroxenite</span> Igneous rock

Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both types of pyroxenes. Closely allied to this group are the hornblendites, consisting essentially of hornblende and other amphiboles.

<span class="mw-page-title-main">Ultramafic rock</span> Type of igneous and meta-igneous rock

Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.

<span class="mw-page-title-main">Lamprophyre</span> Ultrapotassic igneous rocks

Lamprophyres are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide, and high nickel and chromium.

<span class="mw-page-title-main">Volcanic pipe</span> Subterranean geological structure formed by volcanic eruption

Volcanic pipes or volcanic conduits are subterranean geological structures formed by 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, 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 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.

<span class="mw-page-title-main">Lamproite</span> Mantle rock expulsed to the surface in volcanic pipes

Lamproite is an ultrapotassic mantle-derived volcanic or subvolcanic rock. It has low CaO, Al2O3, Na2O, high K2O/Al2O3, a relatively high MgO content and extreme enrichment in incompatible elements.

<span class="mw-page-title-main">Lherzolite</span>

Lherzolite is a type of ultramafic igneous rock. It is a coarse-grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser amounts of calcic chromium-rich clinopyroxene. Minor minerals include chromium and aluminium spinels and garnets. Plagioclase can occur in lherzolites and other peridotites that crystallize at relatively shallow depths. At greater depth plagioclase is unstable and is replaced by spinel. At approximately 90 km depth, pyrope garnet becomes the stable aluminous phase. Garnet lherzolite is a major constituent of the Earth's upper mantle. Lherzolite is known from the lower ultramafic part of ophiolite complexes, from alpine-type peridotite massifs, from fracture zones adjacent to mid-oceanic ridges, and as xenoliths in kimberlite pipes and alkali basalts. Partial melting of spinel lherzolite is one of the primary sources of basaltic magma.

<span class="mw-page-title-main">Komatiite</span> Magnesium-rich igneous rock

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.

<span class="mw-page-title-main">Ultrapotassic igneous rocks</span> Class of rare ultramafic or mafic igneous rocks rich in potassium

Ultrapotassic igneous rocks are a class of rare, volumetrically minor, generally ultramafic or mafic silica-depleted igneous rocks.

Normative mineralogy is a calculation of the composition of a rock sample that estimates the idealised mineralogy of a rock based on a quantitative chemical analysis according to the principles of geochemistry.

<span class="mw-page-title-main">Wyomingite</span> Type of volcanic rock

Wyomingite is a type of volcanic rock. Specifically, it is a diopside-leucite phlogopite lamproite. It is a potassium enriched, alkaline, basic, phonolite first found in the Leucite Hills of Sweetwater County, Wyoming. Wyomingites are between foidite and tephri-phonolite in composition (in the QAPF classification) and contain leucite (20-25%), augite, phlogopite, apatite, calcite, magnetite and small amounts of olivine (but the latter may be absent). Silica (SiO2) content is between 48.9% and 51.7%. Common groundmass includes potassium-richterite. Wyomingite has also been found at two locations in Australia: West Kimberley, and near Ballina, New South Wales.

<span class="mw-page-title-main">Lake Ellen Kimberlite</span> Geological formation

The Lake Ellen Kimberlite is a poorly exposed volcanic breccia located about 10 miles (16 km) northeast of Crystal Falls in the Upper Peninsula of Michigan. The first publication in 1981 describing the feature led to speculation that this or similar kimberlites in the area might have been the source of the diamonds discovered a century before in Wisconsin as well as a period of exploration by several minerals firms.

<span class="mw-page-title-main">Elliott County Kimberlite</span>

The Elliott County Kimberlite was discovered in Elliott County, Kentucky, by Albert R. Crandall in 1884 over two years before Carvill Lewis named a similar porphyritic peridotite occurring near Kimberley, South Africa, a kimberlite. It occurs as three separate elongate intrusive bodies 1/4 to 1/2 mi in length and a few hundred feet in width, within an area of about a square mile. The rock is a dark-green peridotite (kimberlite) composed of serpentinized olivine and a number of accessory minerals, including phlogopite, pyrope, calcite, enstatite, magnesian ilmenite, and others. Xenoliths, mainly of shale, and igneous rock inclusions are abundant in the three intrusive bodies as described by William Brown in 1977. Detailed petrographic descriptions of the peridotite are presented by Diller in 1887 and Bolivar in 1982. The peridotite has been dated to Early Permian time by K-Ar and Rb-Sr dating of xenocrystic biotite from one of the intrusive masses, however more recent evidence points to a Cretaceous emplacement. The rock is relatively nonresistant, is commonly disintegrated to as much as 50 feet, and usually asserts no topographical expression. Unweathered rock is hard, dark greenish black and weathers to grayish olive. The saprolite is yellowish to reddish brown and strewn with garnet and ilmenite fragments and xenoliths. Several attempts have been made to find diamonds in the kimberlite with no success.

The Igwisi Hills are a volcanic field in Kaliua District of Tabora Region of Tanzania. Three tuff cones are found there, one of which is associated with a lava flow. They are one of the few locations of possibly kimberlitic lava flows on Earth.

<span class="mw-page-title-main">Navajo volcanic field</span> Volcanic field in southwestern United States

The Navajo volcanic field is a monogenetic volcanic field located in the Four Corners region of the United States, in the central part of the Colorado Plateau. The volcanic field consists of over 80 volcanoes and associated intrusions of unusual potassium-rich compositions, with an age range of 26.2 to 24.7 million years (Ma).

References

  1. ↑ Bergman, Steven C. (1987). "Lamproites and other potassium-rich igneous rocks: a review of their occurrence, mineralogy and geochemistry". Geological Society, London, Special Publications. 30 (1): 103–190. Bibcode:1987GSLSP..30..103B. doi:10.1144/GSL.SP.1987.030.01.08. S2CID   129449668.
  2. ↑ Clement, C. R., 1982: A comparative geological study of some major kimberlite pipes in the Northern Cape and Orange free state. PhD Thesis, University of Cape Town.
  3. ↑ Clement, C. R., and Skinner, E. M. W. 1985: A textural-genetic classification of kimberlites. Transactions of the Geological Society of South Africa. pp. 403–409.
  4. ↑ Sparks, R.S.J. (2013-05-30). "Kimberlite Volcanism". Annual Review of Earth and Planetary Sciences. 41 (1): 497–528. Bibcode:2013AREPS..41..497S. doi:10.1146/annurev-earth-042711-105252. ISSN   0084-6597.
  5. ↑ "kimberlite eruption | volcanism | Britannica". www.britannica.com. Retrieved 2022-07-14.
  6. ↑ Kjarsgaard, B. A. (2007). "Kimberlite pipe models: significance for exploration" (PDF). In Milkereit, B. (ed.). Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploratio. Decennial Mineral Exploration Conferences, 2007. pp. 667–677. Archived from the original (PDF) on 3 August 2021. Retrieved 1 March 2018.
  7. ↑ Wagner, P. A., 1914: The diamond fields of South Africa; Transvaal Leader, Johannesburg.
  8. ↑ Smith, C. B., 1983: Lead, strontium, and neodymium isotopic evidence for sources of African Cretaceous kimberlite, Nature, 304, pp. 51–54.
  9. ↑ Mitchell, Roger Howard (1995). Kimberlites, Orangeites, and Related Rocks. Boston, MA: Springer US. ISBN   978-1461519935.
  10. ↑ Sarkar, Soumendu; Giuliani, Andrea; Dalton, Hayden; Phillips, David; Ghosh, Sujoy; Misev, Sarah; Maas, Roland (2023-06-20). "Derivation of Lamproites and Kimberlites from a Common Evolving Source in the Convective Mantle: the Case for Southern African 'Transitional Kimberlites'". Journal of Petrology. 64 (7). doi:10.1093/petrology/egad043. ISSN   0022-3530.
  11. ↑ Francis, Don; Patterson, Michael (April 2009). "Kimberlites and aillikites as probes of the continental lithospheric mantle". Lithos. 109 (1–2): 72–80. Bibcode:2009Litho.109...72F. doi:10.1016/j.lithos.2008.05.007.
  12. ↑ Nixon, P.H. (March 1995). "The morphology and nature of primary diamondiferous occurrences". Journal of Geochemical Exploration. 53 (1–3): 41–71. Bibcode:1995JCExp..53...41N. doi:10.1016/0375-6742(94)00034-9. ISSN   0375-6742.
  13. ↑ CAMERON, E. M. (September 1994). "Depletion of gold and LILE in the lower crust: Lewisian Complex, Scotland". Journal of the Geological Society. 151 (5): 747–754. Bibcode:1994JGSoc.151..747C. doi:10.1144/gsjgs.151.5.0747. ISSN   0016-7649.
  14. ↑ Stachel, T.; Harris, J.W. (September 2008). "The origin of cratonic diamonds — Constraints from mineral inclusions". Ore Geology Reviews. 34 (1–2): 5–32. Bibcode:2008OGRv...34....5S. doi:10.1016/j.oregeorev.2007.05.002. ISSN   0169-1368.
  15. 1 2 Kjarsgaard, Bruce A.; Januszczak, Nicole; Stiefenhofer, Johann (2019-12-01). "Diamond Exploration and Resource Evaluation of Kimberlites". Elements. 15 (6): 411–416. Bibcode:2019Eleme..15..411K. doi:10.2138/gselements.15.6.411. ISSN   1811-5217.
  16. ↑ H.O. Cookenboo, H.S. Grütter; Mantle-derived indicator mineral compositions as applied to diamond exploration. Geochemistry: Exploration, Environment, Analysis 2010;; 10 (1): 81–95.
  17. ↑ McClenaghan, B., Peuraniemi, V. and Lehtonen, M. 2011. Indicator mineral methods in mineral exploration. Workshop in the 25th International Applied Geochemistry Symposium 2011, 22–26 August 2011 Rovaniemi, Finland. Vuorimiesyhdistys, B92-4, 72 pages.
  18. ↑ Soloveichik, Yury G.; Persova, Marina G.; Sivenkova, Anastasia P.; Kiselev, Dmitry S.; Simon, Evgenia I.; Leonovich, Daryana A. (2023-11-10). "Comparative Analysis of Airborne Electrical Prospecting Technologies Using Helicopter Platforms and UAVs when Searching for Kimberlite Pipes". 2023 IEEE XVI International Scientific and Technical Conference Actual Problems of Electronic Instrument Engineering (APEIE). IEEE. pp. 1–4. doi:10.1109/APEIE59731.2023.10347567. ISBN   979-8-3503-3088-5.
  19. ↑ Lépine, Isabelle; Farrow, Darrell (2018-12-01). "3D geological modelling of the Renard 2 kimberlite pipe, Québec, Canada: from exploration to extraction". Mineralogy and Petrology. 112 (2): 411–419. Bibcode:2018MinPe.112..411L. doi:10.1007/s00710-018-0567-x. ISSN   1438-1168.
  20. ↑ Hetman, C. M.; Diering, M. D.; Barnett, W. (2017-09-18). "Generation of 3D kimberlite pipe models for resource classification and mine planning: Data sources, procedures, and guidelines". International Kimberlite Conference Extended Abstracts: 2017. Vol. 11. doi:10.29173/ikc4005. ISBN   978-1-55195-425-7.{{cite book}}: |journal= ignored (help)
  21. ↑ Torsvik, Trond H.; Burke, Kevin; Steinberger, Bernhard; Webb, Susan J.; Ashwal, Lewis D. (July 2010). "Diamonds sampled by plumes from the core–mantle boundary". Nature. 466 (7304): 352–355. Bibcode:2010Natur.466..352T. doi:10.1038/nature09216. ISSN   1476-4687.
  22. ↑ Janse, A. J. A. (Bram) (2007-06-01). "Global Rough Diamond Production Since 1870". Gems & Gemology. 43 (2): 98–119. doi:10.5741/gems.43.2.98. ISSN   0016-626X.
  23. ↑ Dasgupta, Rajdeep; Hirschmann, Marc M. (2010-09-15). "The deep carbon cycle and melting in Earth's interior". Earth and Planetary Science Letters. 298 (1): 1–13. Bibcode:2010E&PSL.298....1D. doi:10.1016/j.epsl.2010.06.039. ISSN   0012-821X.
  24. ↑ Torsvik, Trond H.; Cocks, L. Robin M. (January 2013). "Chapter 2 New global palaeogeographical reconstructions for the Early Palaeozoic and their generation". Geological Society, London, Memoirs. 38 (1): 5–24. doi:10.1144/m38.2. ISSN   0435-4052.
  25. ↑ "Diamond investing FAQ". MINING.com. 18 February 2014. Retrieved 30 August 2017.
  26. ↑ "Kimberlite Deposits and Geology Formation of Diamonds". 2015-10-16. Retrieved 2024-04-11.
  27. ↑ Schumann, W. (2006). Gemstones of the World. Sterling. p. 88. ISBN   978-1-4027-4016-9 . Retrieved 2022-07-15.
  28. ↑ "South Africa: A New History of the Development of the Diamond Fields" (1902): New York Times Archives, New York Times.

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