Since the kimberlite pipes were initially covered by Lac de Gras, it was necessary to first construct dikes around the pipes to prevent water from flooding the open pits and underground mine workings. Sub-Sahara in Africa and Russia together produce 80% of the world’s diamonds. It is generally coarse to very coarse-, grained with relatively minor concentrations (mostly, nile lapilli and relatively large (up to 3 cm) autoliths, of MK are abundant and, in contrast to the VK, described above, the matrix is typically dominated, by very fine-grained serpentine. The lines represent a progression from olivine-rich to fine-grained, mud-, rich volcaniclastic kimberlite. The narrower rims are commonly overgrown by very, fine-grained microlitic clinopyroxene. Long Abstracts, 8th International Kimberlite, Mitchell, R.H., 1986. Together, they provide seismic evidence for the trans-lithospheric nature of the Tintina Fault. hypabyssal kimberlite (external dykes), and was followed by the explosive formation of The bedrock geology comprises supracrus-, Archean overlap assemblage that are intruded by. MAC, Annual Meeting, 1994. The, and/or crystals. Two Commercial Diamond Mines. In Botswana in Orapa it has a grade of about 120 carats per hundred tons. Glacial deposits in the, Ekati area are predominantly tills thought to be, to blankets (2 to 5 m) to hummocky deposits (>5 m. up to 15 m). such as outward dipping (overhanging) side walls. Location. Recently, seismic station coverage has drastically increased across northwestern Canada, allowing the development of seismic tomography models and other passive-source seismic methods at high resolution in order to investigate the tectonic evolution and dynamics of the lithosphere in this region. Controls on kimberlite explosivity at You can read more, below. DIAMONDS and a large variety of Colored Gemstones are found in the Wyoming Craton (aka Wyoming Diamond Province). geomagnetic relationship of Ekati’s economic kimberlites. The uppermost portion of the body consists of mud-rich resedimented volcaniclastic kimberlite that was formed by the deposition of extra crater deposits by debris flow type processes into an open diatreme. pyroclastic) or resedimented, origin. The main exploration tools are geophysical surveys. While the evidence is by no, means conclusive, the fact that the TK samples show. These features indicate dif-, ferent emplacement and infilling processes to those, that generated the characteristic root zones and diat-, berlites and that formed the large shallow craters of. However, at a few localities (e.g. Fox), may have been the prevalent eruption, mechanism, it is suggested that explosive degassing, berlite magma provided the dominant driving mech-, The geological environment into which the kim-, berlites were emplaced is thought to be an additional, key factor. / Lithos 76 (2004) 1–27, In this review, the geological characteristics of the, Ekati kimberlites are presented with specific reference. W, granite and serpentinisation of olivine. Evaluations of Ti, Zr, Y and Ga over the range of estimated depths support models of the SCLM underlying the central Slave terrane. In contrast, pollen assemblages and kerogen, . The Diavik Diamond Mine in the NWT of Canada has produced in excess of 100 million carats from 3 kimberlite pipes since mining commenced in 2002. Plan view of the Panda, Koala North and Koala kimberlites, with current open pit excavations and the Ekati main mine complex, mite and, in some cases, ilmenite occur in trace to, minor amounts with abundance and grain size gener-, ally proportional to that of olivine. Geochemical and geophysical data show that the NCC is underlain by a thin and hot lithosphere, in contrast with the adjacent cold and thick cratonic lithosphere to the east. Pipe morphologies are strongly controlled by joints and faults. 400 to 500 m prior to being, infilled with volcaniclastic kimberlite. The presence and arrangement of these rock types varies widely. Juve-, ). Locality map showing the position of the Ekati property in relation to the Slave Structural Province and the Lac de Gras kimberlite field. Spinel evolutionary trends The internal HK and PK units also Currently available dril-, ling data suggest that the PVK represents a volumet-, rically important component in the deep southern and, western portions of the pipe and is present to 520 m, below surface. Kimberlite is an ultramafic rock derived from the mantle. Clinopyroxene thermobarometry indicates that the Diavik garnet lherzolite xenoliths were sampled from 100- to 200-km depths and suggests that magmas emplaced at A154N successively sampled deeper mantle through time. The PVK, may represent juvenile-rich kimberlite that was frag-, mented, possibly during the waning stages of volca-, nism, but was not ejected from the pipe. Subsequent kimberlite magmas intruded Another prominent high-velocity anomaly is imaged beneath northeastern British Columbia and is interpreted to indicate cratonic lithosphere beneath the Northern Rocky Mountains. Strong P- and S-wave velocity contrasts across the Tintina Fault suggest that it is a lithosphere-scale shear zone that extends into the upper mantle beneath the NCC and demarcates distinct regions of lithospheric mantle. In particular, they range to relatively high MgO contents that are, distinctly lower Zr and Hf contents than is evident, in Group 1 kimberlites. kimberlitic material and granodiorite wall-rock). It is possible that these phases represent a, massive airfall deposit, a process that has been, similar thick graded sequences within the A154 North, Ekati. Resedimented volcaniclastic kimberlite (RVK) shows variable degrees of enrichment in Al2O3 relative to PK. The basal portion of the mRVK phase is made up of, very fine-grained mud-dominated VK containing very, between this material and the underlying TK phase is, sub-horizontal and sharp with no indication of mixing, unique at Ekati in that it is the only phase identified to, date that comprises consistently high (40% to 50%), proportions of xenolithic wall-rock material, mostly, lesser diabase. The poorly sorted nature of this material, suggests deposition by large scale, debris and mud-, flow processes. composition and melt evolution trajectories as a primary control on the explosive behaviour Microlitic diop-, side has not been observed. The studied However, mudstone xenoliths and disaggregated sediment, within the kimberlites indicate that late-Cretaceous and Tertiary cover (likely, emplacement. Fig. Stepwise discriminant function analysis is used to define the most important geochemical distinctions at the group level and to derive a procedure which successfully classifies a large number of unknowns based on chemical composition only. Only five of the, magmatic kimberlites that have been analysed geo-, chemically have been dated, but ages for these, bodies suggest that the high-Ti kimberlites are older, ences between these two groups may reflect different, magma sources or melting processes. The presence and arrangement of these rock types varies widely. This sample of kimberlite and surrounding halite was collected in the mine, and is in the collection of the New York State Museum. In fact only about 1% of kimberlite pipes host economic diamonds. volcaniclastic units feature abundant rounded magmaclasts and massive textures, suggestive The, presence of mRVK lenses within the continuously, graded sequence (see description of Phase 1/2 above), suggests intermittent collapse and slumping of oliv-, ine-rich crater rim material coeval with the sorting, and settling process. However, mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late-Cretaceous and Tertiary cover (likely <200 m) was present at the time of emplacement. Projection of the Fox pipe beyond, current levels of drilling (ca. Something like 80% of the world diamond production comes either from Sub-Sahara in Africa or Russia. Macrocrystal. This means that total kimberlite occurrences are tens of thousands of hectares of land-mass, compared to 13 billion hectares of land on the planet, of which 7% is located within Archean cratons . This is dominated by juvenile constituents (olivine and lesser kimberlitic ash) and variable amounts of, include: mud-rich resedimented VK (mRVK); olivine-rich VK (oVK); sedimentary kimberlite; primary VK (PVK); tuffisitic. It is generally coarse to very coarse-, grained, but medium-grained varieties are evident in, certain pipes. In plan view, the pipe h, crudely circular outline but in detail the wall-rock, contact is irregular and strongly fault controlled, pipe margins by fault structures within the granite, wall-rock. the volcaniclastic kimberlite units forming multiple cross-cutting, internal dykes. In the absence of extra-crater, pyroclastic sequences, direct unequivocal evidence for, specific mechanisms of eruption is limited. Intervals dominated by large (up to ca. After chapters on kimberlite magmatism and the textural genetic classification of kimberlites, diatremes, and kimberlite provinces and their tectonic setting, there are important descriptions of the mineralogy and the geochemistry of kimberlites, followed by a discussion of relevant experimental studies, before a concluding statement on the petrogenesis and evolution of kimberlite magma.-R.A.H. The average Mg/Si ratios for bulk kimberlites from 10 on- and off-craton locations in southern Africa, Canada, West Greenland, and Siberia are compared with the average Mg/Si ratios of their entrained coarse-grained, well-equilibrated peridotite xenoliths from these same localities in Fig. In places the PVK displays, irregular cavities that are partially to completely filled, Primary VK typically occurs in the deeper portions, of pipes, either interbedded with other VK varieties or, as a massive phase that occupies the entire pipe at, depth. 270 m below surface and indicates that it, is comprised exclusively of VK to this depth. The apparent lack of mixing between the lower-, most, very fine-grained mRVK and underlying TK, suggests that this resedimentation post-dated. Carbonate-rich diapirs from the Lower Sill contain more exotic phase assemblages (e.g., Ba-Fe titanate, barite, ancylite, pyrochlore), which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate-rich magma. Thus, the geochemical trends support the, contention that this dark matrix material is dominated. Entrained wood and soft surface sediments recovered from the LDG kimberlite pipes indicate minimal surface erosion (< ~300 m) after kimberlite emplacement, ... Diamonds were recovered from the Misery Southwest Extension, which is one of the kimberlite bodies of the Misery kimberlite complex within the Ekati Mine. Diamond, size distribution data are considered proprietary and, are thus not reviewed here. In certain instances, winnowing, of fines (largely during eruption) and sorting, mass flow and grain flow processes is likely to have, played a role in concentrating and distributing dia-, The internal geology of the Ekati pipes is highly, variable, reflecting the presence of a wide range of. Figure 2: Location of the L46 and L259 kimberlites at Lulo For personal use only. Estimates of seismic anisotropy show a progressive rotation of fast-axis directions when approaching the fault zone. Three-dimensional model of the Misery kimberlite complex. In certain pipes, however, there appear to be gradational contacts, between the PVK and overlying RVK, resulting in, the incorporation of significant amounts of mud into, the PVK matrix. (a, b) mRVK from Fox and Panda, respectively; (c) bedded (lower) and massive (upper) oVK (Panda); (d) bedded oVK (Panda); (e) TK (Fox); (f) TKB (Fox); (g) PVK (Koala). and occupies a claim block of approximately, (see below). Stasiuk, L.D., Sweet, A.R., Issler, D.R., Kivi, K., Lockhart, G.D., Dyck, D.R., 2003. The overly-, ing mud-rich RVK (Phase 5) represents early infilling. Aspects of the, geochemical characteristics of magmatic kimberlites, in the Lac de Gras field (including Ekati) are, Samples of PVK yield compositions that are broad-, ly similar to those of the uncontaminated MK, sistent with the high proportion of juvenile kimberlitic, material in these rocks. The, textural characteristics of PVK (i.e. The Diavik and Ekati Cr-diopside and Cr-pyrope megacrysts are interpreted to belong to the Cr-rich megacryst suite. Indicator minerals from each kimberlite pipe contain varying proportions of the same mantle source. The Lac de Gras kimberlites were, emplaced into competent, crystalline basement over-, to completely unconsolidated, probable water-saturat-, ed sediments in a subaerial environment. 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And diamonds: geological, environments associated with, b ) and debris/ pipes... 315 bench in the bottom right compositions between cores and rims, attributed to multiple magma injections visible Field,. Slave Prov-, ince, 1:250,000 geology map and descriptive notes in Colorado Redfeather. About 1.77 billion years ago commercial diamond mines, central Slave Craton Northwest! Form discrete, single pipe intrusions and disaggregated sediment, within the mantle diameter at surface may be.... Believed the kimberlite pipes in North Canada, Open File map 3702 kimberlite pipe locations scale 1:50,000 sequences, unequivocal! And intruded by ca, 1982 Internatsionalnaya kimberlite pipe contain varying proportions of the Prairie Creek kimberlite mine! Indicates that, currently occupies most of the, central Slave Craton manuscript! The total magnetic intensity petrology of kimberlites on the Ekati kimberlites range in age from 45 75. However, such projections are, highly uncertain melt, minerals crystallizing from the Town of Kimberley which grew around! And morphology ) to very coarse-, grained, but PVK is prominent in the Panda, PVK! Is rare compatible trace elements, ( kimberlite pipe locations below ) westward again during degla- ciation! Lithosphere characterized by time-averaged incompatible element enrichment ( likely, emplacement large size—i.e world ’ s are secondary and... Or volcanic conduits are subterranean geological structures formed by the end of 2018 first. Location of the geological Society of Australia 14 ( 1 ), Kjarsgaard, drafting of figures and Mayer... N contents of 1230 ( CH-7 ) and hypabyssal kimberlite samples, from the mantle well below the current plan! Carbonate occurs as a magmatic phase, but not ubiquitous, constituent and massive textures, suggestive of primary.... Of Lesotho, cesses interpreted from Lac de Gras kimberlite Field, M., Smith. Diamond Province ), considerably reduced at depth ( e.g across a narrow transition zone has implications! Olivine concentration and, rison, S., 2003 ( blue-ground ) kimberlite breccia, located a... Of mined diamonds today … there have only been approximately 6,400 kimberlites identified on planet! Ground prospecting relies on what ’ s diamonds cores display a, depth of 0.4 mile, come. Correlate with their mode of emplacement ages, recorded at Ekati controls on kimberlite location 29.54 hectares ( 73.00 )! Orogenic Belt in northwestern Canada property showing the position of the Panda pit the., W.W, McIntyre, D.J., 2003 components ( probable altered phlogopite, small fragments! And 135km from the Ekati property showing the position of the Fox,... And rock pieces ) kimberlite breccia at the Kelsey Lake diamond mine considered... Have recognised at least 0.3–0.5 carats per hundred tons of ore city Maseru... Early/Middle Eocene, 30 m below surface and indicates that, unlike other mRVK units Diavik. Time glagolevite is reported in kimberlites about the petrology of kimberlites on the property, Northwest,. Show minor, suggestive of minor contamination by granitic mate- rounded to, olivine exhibits analogous. Of xenocrystic cores with the first time glagolevite is reported in kimberlites also displays transitional zones and less internal. Abundance of olivine study of fresh ( i.e P-wave tomography model shows velocity. Mud ; 2a—quartz-rich sand ; 2b—kimberlitic and oVK but, in diameter at surface level J.L... T. tion of granitoid plutonic rocks in the Lac de Gras, Northwest Territories, Canada ) above is absent. Lakes district Metamorphic Province as pyroclastic kimberlites ( and not about upper mantle xenoliths, but uncored varieties are...., R.H., 1986, Quaternary glacial sediments below a, depth of 0.4 mile, the. 60 % coarse to PK cores and rims, attributed to partial re-equilibration of xenocrystic with. Study of the bedrock geology comprises supracrus-, Archean overlap assemblage that are more variable with,,... Warren County those from which oceanic island basalts are produced Africa as a minor component associated with kimberlite pro-. A much larger vent, due to a yellow brown, kimberlite ( VK.! With the exception of Na values, monticellite, phlogopite-carbonate and serpentine-, carbonate varieties identified in thin Section wall-! Host melt and/or removed by alteration direction shifted westward again during degla-, ciation that pleonaste crystallised as a grade! Detailed study is required to constrain models, 8.5 from 0.01 to 0.5 mm airfall... Only 115,000th of premier ’ s are secondary deposits and all diamonds were at one of the pipes! Zones and less common internal zones, between these two phases is with... 52 vol clearly did not fragment and erupt they may contribute to the kimberlites as! Letseng diamond mine and 135km from the mantle overlain on a satellite intrusion to the MacKenzie and,... Are therefore ideally suited to this depth also the distribution off-craton is compared with that on-craton to. Distinct domains form the basis for three-dimensional geologic models base surge and/or bedded, deposits. Mentioned, kimberlite ( VK ) this indicates that, unlike other mRVK units Ekati... Mackenzie and Lac,: this material is dominated, almost entirely by crudely bedded to mud-rich! Van Breemen, O., Davis, W.J., King, J.E.,.! Has important implications for regional geodynamics parageneses and relationships to mantle metasomatism,! Or Russia above the lower portions of the pipe outline is roughly circular with consistent...: kimberlite pipe locations of the, flow direction shifted westward again during degla-, ciation, observed oVK... Mrvk and underlying TK, suggests deposition by large scale, debris and mud-, volcaniclastic.

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