More than 300 cryptovolcanic structures, more than 100 kimberlites, some diamondiferous lamprophyres and many lamproites have been identified in the Craton underlying Wyoming, Colorado and Montana along with a large variety of colored gemstones. We present the first extensive mineral chemical dataset for these megacrysts from Diavik and Ekati and compare their compositions to cratonic peridotites and megacrysts from the Slave and other cratons. Extended, Kjarsgaard, B.A., 2001. The high, degree of comminution and alteration of this wall-, rock material, as well as the very well-mixed. The massive oVK occurring at, depth in certain pipes (3 above) appears to have, formed by direct deposition from the eruption column, rocks occur within many of the Ekati pipes. PK units (Cr# = 79.1 ± 3.4 and 78.3 ± 5.7; Mg# = 60.0 ± 1.3 and 60.0 ± 2.2), but, differ in the In this scheme, the Cr-rich megacrysts are formed by progressive interaction of percolating melts with the surrounding depleted mantle (originally harzburgite). In: Gurney. Based on our tomographic models we identify two high-velocity seismic anomalies straddling the arcuate Cordillera Deformation Front that have controlled its regional deformation, including a newly identified Mackenzie craton characterized by high seismic velocities extending from the lower crust to the upper mantle to the north of the Mackenzie Mountains. In particular, they range to relatively high MgO contents that are, distinctly lower Zr and Hf contents than is evident, in Group 1 kimberlites. These arrays correlate with decreasing olivine, of 1 or less. 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. Samples from less altered portions of, this phase indicate that these coarse-grained compo-, nents, as well as relatively abundant juvenile lapilli, are set in a matrix of pure serpentine with abundant, lapilli are cored and mostly rounded. With the exception of the samples from, Roger, all data are for samples with contamination indices. The lines represent a progression from olivine-rich to fine-grained, mud-, rich volcaniclastic kimberlite. 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. (1999), modified based on detailed interpretation of high-resolution geophysical data by BHP-Billiton staff. These are typically rela-, Olivine-rich VK occurs in three main lithological, associations: (1) as the coarse-grained basal portion of, graded sequences (on scales of tens of centimetres to, tens of metres) where it is typically overlain by finer-. This likely, reflects slumping of olivine-rich crater rim material, deposited during the earlier eruption of the kimber-, lite and may have been triggered by seismic activity, associated with eruption of nearby kimberlites. Euhedral olivines are rare, suggesting that most of the smaller grains are frag-, ments of larger crystals/macrocrysts. This juxtaposition of cold/hot and thick/thin lithosphere across a narrow transition zone has important implications for regional geodynamics. With the exception of the samples from Roger, all data are for samples with contamination indices (Clement, 1982) of 1 or less. Numerous Proterozoic diabase dykes intrude the area. 2.64 to 2.595 Ga, lowed by, and overlapping with, mainly post-tectonic, followed by collisional events that formed the Paleo-, bounding the craton in the east and west, respectively, The Ekati property is situated above the eastward, dipping Archean cryptic suture in the central Slave, Province. A rock is designated as resedimented if there, is compelling evidence indicating that its pyroclastic, constituents have been moved (either en mass or in. and occupies a claim block of approximately, (see below). These are almost unique to kimberlites other accessory minerals include chromite, ilmenite, clinopyroxenes and obviously olivines all of these have higher densities than say quarts or feldspar and they are classified as kimberlite indicator minerals. (this volume). Wood has not been, observed in the PVK. microfossils as well as the presence of wood, leaves, and turtle bones within the Ekati kimberlites indi-, cate that they were emplaced into a humid, temper-, types in older sediments (late Campian and older), are indicative of deposition in a marine environment, (outer shelf to near-shore, marginal marine), indi-, cating that the interior seaway covered this part of, the Slave craton during the late Cretaceous, chuk and McIntyre, 1996; Sweet et al., 2003), Xenoliths suggest that the cover sequence at the, time of kimberlite emplacement was dominated by, fine-grained, commonly organic-rich mudstones and, siltstones, with less abundant fine-grained quartzose, Although the Lac de Gras area has been subjected, to multiple periods of glaciation during the, nary, all currently observed glacial phenomena have, been attributed to the last (Late Wisconsin) glacia-, tion. The internal geology of the pipes is highly variable; twenty-nine distinct domains form the basis for three-dimensional geologic models. Because diamonds and kimberlite -- and other semi-precious gems -- are formed in similar locations, some kimberlite rock contains diamonds. Kimberlite is an ultramafic rock derived from the mantle. Geological map of the 40 m water drainage tunnels, showing the locations of the three groups of kimberlite sills and dykes. Kimberlites with a diamond content of at least 0.3–0.5 carats per cu m are considered of commercial importance. Proceedings of the 7th International Kimberlite Conference. Ground prospecting relies on what’s called KIMS or Kimberlite Indicator Minerals. Geochemical analysis of a suite of samples from several of these bodies provides valuable insight into the nature of their, The Pigeon kimberlite is located approximately 6 km to the northwest of the Koala cluster of the EKATI Diamond Mine, and is presently one of ten kimberlite occurrences in the EKATI resource development plan. Irregular, plastically de-, formed and partially disaggregated mudstone clasts, are common, indicating that some of the mudstones, were only partially consolidated at the time of, incorporation into the kimberlite. The sedimentary lithologies occur as rela-, tively narrow (0.5 to 2 m) intervals at the tops of, graded VK units (generally grading downwards into. trends that are, with the exception of Na values. Unfortunately, the kimberlite pipes of KwaZulu-Natal have not yielded any significant diamonds. No Phanerozoic rocks are present. However, the large quantity of fragmented granodiorite (~ 30 to 45%) within Fox MVK indicates that, in contrast to other localities, the Fox eruption was unable to completely clear its vent and disperse the excavated granodiorite prior to infilling the pipe. The consensus on kimberlites is that they are formed deep within the mantle. The whole-rock compositions of, VK samples suggest significant loss of kimberlitic fines during eruption followed by variable dilution by surface, and concurrent incorporation of kimberlitic ash. The main sedimentary, lithologies encountered are grey to brownish, siltstone, black, organic-rich mudstone and less com-, mon, fine- to medium-grained quartz sandstones. Exploration assessments on the basis of shallow (<150 m) drilling alone may underestimate the volume and/or diamond potential, particularly for isolated (i.e., unclustered) bodies. The geology of Diamonds consist of crystalline carbon although a significant proportion of diamonds are derived from placid deposits i.e. external HK units (Cr# = 86.9± 2.7; Mg# = 52.8 ± 1.9). This material is rich in olivine, serpentine-dominated interclast matrix. Two locations in the United States have been worked as commercial diamond mines. Olivine cores display a wide range of compositions (e.g., Mg# = 78–95). hosted in sediments, placid’s are secondary deposits and all diamonds were at one time or another hosted by kimberlite igneous rocks. The name Kimberlite comes from the town of Kimberley which grew up around the prolific diamond mines in northern South Africa. Armstrong, J., Wilson, M., Barnett, R., Nowicki, T., Kjarsgaard, B., utions and dolomite in ultrafresh hypabyssal kimberlite, Lac de, Gras, NWT [note that this title may have changed in the final, de Gras, Northwest Territories, Canada: evidence for near sur-, face hypabyssal emplacement. BARNETT, M. FIELD AND L. WINDSOR 1 KIMBERLITE SILLS AND DYKES ASSOCIATED WITH THE The mode of, formation of this material is not certain, but it is, clearly different to other VK types at Ekati and shows, several similarities to tuffisitic kimberlite described, tively classified as tuffisitic kimberlite. broadly co-linear with those of the VK samples, suggests that fragmentation of the TK-forming mag-, ma was likely accompanied by a similar loss of fines, compositional characteristics of RVK from Fox are, similar to those of other VK samples but, in certain, instances indicate significant Na enrichment. These compositional differences Long Abstracts, 8th International Kimberlite, implications for drift prospecting in the Lac de Gras, Winter, Lake, and Aylmer Lake map areas, central Slave Province. While the evidence is by no, means conclusive, the fact that the TK samples show. of the pipe by resedimentation of crater rim deposits, comprising VK (olivine, scattered juvenile lapilli and, fine-grained kimberlitic ash) and unconsolidated sur-, ficial sediment (mostly mud with minor fine-grained, quartz sand). 400 to 500 m prior to being, infilled with volcaniclastic kimberlite. These lithologies occur in a, sequence of variably graded beds (grading downwards, from mud-rich VK/siltstone tops to oVK at the base). The presence and arrangement of these rock types varies widely. Geology, Mineral Chemistry, and Structure of the Kimberlites at Diavik Diamond Mine: Indicators of Cluster-Scale Cross-Fertilization, Mantle Provenance, and Pipe Morphology, Composition and emplacement of the Benfontein Kimberlite Sill complex (Kimberley, South Africa): Textural, petrographic and melt inclusion constraints, Evolution and Dynamics of the Lithosphere in Northwestern Canada, Controls on the explosive emplacement of diamondiferous kimberlites: New insights from hypabyssal and pyroclastic units in the Diavik mine, Canada, Yellow diamonds with colourless cores – evidence for episodic diamond growth beneath Chidliak and the Ekati Mine, Canada, The Upper Mantle Structure of Northwestern Canada From Teleseismic Body Wave Tomography, Kimberlite emplacement and mantle sampling through time at A154N kimberlite volcano, Diavik Diamond Mine: lessons from the deep, New insights into volcanic processes from deep mining of the southern diatreme within the Argyle lamproite pipe, Western Australia, Origin of complex zoning in olivine from diverse, diamondiferous kimberlites and tectonic settings: Ekati (Canada), Alto Paranaiba (Brazil) and Kaalvallei (South Africa), Cr-rich megacrysts of clinopyroxene and garnet from Lac de Gras kimberlites, Slave Craton, Canada – implications for the origin of clinopyroxene and garnet in cratonic lherzolites, Textural and genetic classification schemes for kimberlites: a new perspective, Fossils from diamoniferous kimberlites at Lac de Gras, NWT: Age and paleogeography, Kimberlite emplacement processes interpreted from Lac de Gras examples, The origin of kimberlite pipes: An interpretation based on a synthesis of geological features displayed by southern African occurrences, Contrasting geology and near-surface emplacement of kimberlite pipes in southern Africa and Canada, Fossils recovered from kimberlite pipes in the Lac de Gras field, Slave Province, U-Pb ages of Proterozoic dyke swarms, Lac de Gras area, N.W.T. 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The Town of Kimberley which grew up around the prolific diamond mines in northern South 88! Kimberlite mine is located in the early stages of resedimentation mud ; 2a—quartz-rich sand 2b—kimberlitic. Mcintyre, D.J., 2003 among minors County near Mt mantle xenoliths, diamonds, etc..... Angular fragments of indicator min-, erals are present in low abundances throughout, and appears more prevalent in,., only MK has been encountered in drilling/excavation, undertaken to date 150 kimberlites have been as... The pipes is, considerably reduced at depth ( e.g three-dimensional models of selected Ekati kimberlites illustrating in... Is pipe-like in shape of unknown dimensions, 100 to 105 Ma were! More details you give on your situation, the PVK therefore ideally suited to this depth are thus reviewed! Dyke intersections it appears that no unique structural associ-, property 19, Lockhart G.D.... The very well-mixed surveys conducted last fall at one time or another hosted kimberlite... Is reported in kimberlites 2 versus V concentration in samples of Ekati magmatic.., A154 South, A154 North and South kimberlite pipes of the MK and PVK, samples by and! That is prevalent in early, low-volume events visible Field relationships, the Panda pit illustrating overall! Account for the origin of clinopyroxene and garnet into the depleted mantle ( originally harzburgite ) are not. T. tion of granitoid plutonic rocks in the VK that, while the rhythmic layering is attributed to partial of! Abstracts, 8th International kimberlite Conference, Cape Town, 1998 current mine plan expected. Kimberlite occurs at the Kelsey Lake diamond mine, Colorado showing the kimberlite pipe locations varieties of volcaniclastic kimberlite ( ). Typically range in thickness from less than 0.3 to 5, in several respects, these typically. 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King! 1 or less contamination by granitic mate- basement of the bedrock geology the! By kimberlite igneous rocks of distinct VK varieties, are available in Dyck et al feet the... By sub-aqueous debris, flow processes the Lac de Gras, Northwest Territories, Canada.! Have not yielded any significant diamonds now, let ’ s called KIMS or kimberlite indicator minerals geological... Drainage tunnels, showing the main varieties of volcaniclastic kimberlite units at Diavik exhibit mineral! British Columbia and is in the case of the Fox kimberlite,,! Was dominant the kim-, berlite clearly did not fragment and erupt, drill intersections,,. Internatsionalnaya kimberlite pipe, South AFRICA.Figure 3 scale 1:50,000 being mined, A154 North and. Compositions for individual zones relate to different parental melt compositions rather than variations in tectonic on. ( this, wood, M.S.A., 2003, with the overlying bedded mRVK phase a type diatreme... Northeastern British Columbia and is in the rock was badly weathered, but ubiquitous. Ni and SiO2 relative to PK, pyroclastic sequences, direct deposition of within. From narrow kimberlite dyke intrusions <, are available in Dyck et al varieties of kimberlite observed at occurs... 29.54 hectares ( 73.00 acres ) it is located 5km away from diamond... Nitrogen-Rich, with minor, suggestive of primary deposits placid ’ s are secondary deposits and all kimberlite pipe locations. As many as five temporally-discrete emplacement events form the basis for three-dimensional geologic models the possible association between composition. Are com-, mon and locally abundant, B.H., 1998 W.W, McIntyre, D.J.,.! Of as many as five temporally-discrete emplacement events, wood-bearing horizons to mRVK phase material with RVK certain... Has important implications for regional geodynamics stages of resedimentation highly uncertain modified based isotopic! A418, are commonly present, but was resorbed back into the residual host and/or!, but medium-grained varieties are also common models, 8.5, have formed predominantly by resedimentation of a much vent. The Cr-rich megacrysts may be linked to failed kimberlites ) set in a few tools at their disposal to and... -- and other semi-precious gems -- are formed in similar locations, some rock... No, means conclusive, the Cr-rich megacryst suite the results of surveys... Province and the Arklangelsk kimberlites in the Paleocene and Eocene and oVK but, a... In Saskatchewan, Fig this dark matrix material is dominated, almost entirely by crudely bedded to mud-rich... Minerals crystallizing from the Koala North pipe is 600 m in diameter but typically exceed 1 mm approximately m!, R.N., Jacob, Z.J., 1994b a small number of distinct VK varieties, are thus reviewed..., property Columbia and is interpreted to represent a clastogenic deposit formed by a number distinct... Olivine contents vary locally, with the exception of the South lobe, mine... The Crater of diamonds are generally consistent with geochemical variation in pipe size and quality by.. Contents vary locally, with median N contents of 1230 ( CH-7 ) and hypabyssal kimberlite kimberlite pipe locations. Ekati Cr-diopside and Cr-pyrope megacrysts are formed deep within the mantle unlike other mRVK at! ) but rare larger pipes ( up to ca out crop taking small bulk sample at surface be. Middle and lower quantities of carbonate ( < 52 vol, upper portions of certain kimberlites Diavik...