These volcanic explosions produce vertical columns of rock that rise from deep magma reservoirs. 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. 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.
Two Jurassic kimberlite dikes exist in Pennsylvania. The other, the Dixonville-Tanoma Dike in central Indiana County, does not outcrop at the surface and was discovered by miners.
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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. 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.
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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 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. 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.
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. 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.
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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. These indicator minerals are generally sought in stream sediments in modern alluvial material. Their presence may indicate the presence of a kimberlite within the erosional watershed that produced the alluvium. Kimberlites are the most important source of primary diamonds.
Many kimberlite pipes also produce rich alluvial or eluvial diamond placer deposits. About 6, kimberlite pipes have been discovered in the world, of those about have been classified as diamondiferous, and of those just over 30 have been economic enough to diamond mine. The deposits occurring at Kimberley , South Africa , were the first recognized and the source of the name.
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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 ". The blue and yellow ground were both prolific producers of diamonds. Initially, a core drilling programme will be undertaken to determine the width and extent of the dyke system. Once the core drilling programme has been completed a mini-bulk sample of at least tonnes will be undertaken to confirm and determine the diamond content for the kimberlite.
In addition, following the Marsfontein model where an enlargement was discovered on a diamondiferous dyke system, a programme to search for an enlargement on the MAL dyke system has commenced. Soil sampling will be extended to the north and the south of the current sampling grid. An extended groundmagnetic survey has produced an anomaly of approximately 1.
A detailed soil sample programme over the groundmagnetic anomaly has been initiated. Kimberlite dykes have been successfully mined in South Africa for more than sixty years.
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The Bellsbank dykes have been mined for diamonds since Enlargements in the form of small pipes have been found at Bellsbank, Star and Marsfontein. Due to large sample backlogs at laboratories, analytical results from the drilling conducted earlier in the year have not been received. Results will be announced once the analytical data is available and has been assessed. Quality Control and Quality Assurances Quality assurance procedures, security, transport, storage, and processing protocols conform to chain of custody requirements.
Fenn, the third child and eldest son of a butler, Charles Fenn, was largely self-educated, teaching himself French, German and Italian. After studying at Battersea Training College for Teachers —54 , he became the master of a national school at Alford, Lincolnshire. He later became a printer, editor and publisher of short-lived periodicals, before attracting the attention of Charles Dickens and others with a sketch for All the Year Round in He contributed to Chambers's Journal and Once a Week.
In , he wrote a series of articles on working-class life for the newspaper The Star. These were collected and republished in four volumes. Excerpt from Add to Cart. Log in to rate this item. You must be logged in to post a review. Please log in. There are no reviews for the current version of this product Refreshing There are no reviews for previous versions of this product. First Name.
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