Sam ple locations are also shown. Koala). It encompasses the, BHP Billiton Ekati diamond mine and includes 150, kimberlites that form a significant proportion of the, Lac de Gras kimberlite field. The internal geology of the kimberlites ranges from simple single-phase pipes (RVK or MK), to complex bodies with multiple, distinct units of VK. 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. Something like 80% of the world diamond production comes either from Sub-Sahara in Africa or Russia. The red area in the center indicates the strongest magnetic readings. In particular, they range to relatively high MgO contents that are, distinctly lower Zr and Hf contents than is evident, in Group 1 kimberlites. respectively), with a marginally lower Mg# of 90.2 ± 0.2 in olivine rims from the external the mudstone) is occupied primarily by a largely, continuous graded sequence of VK (Phase 1), which, grades with depth from homogeneous fine-grained, silty to sandy kimberlite containing abundant exotic. Leslie, Grizzly, Pigeon), a large proportion of the pipe is occupied by, MK. The Lower Sill is characterised by carbonate-rich diapirs, which intrude into oxide-rich layers from underlying carbonate-rich levels. possible association between magma composition and intrusion age. of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions. Within significantly dia-, mondiferous kimberlites, there is a close correlation, between grade and the abundance and grain size of, coarse, macrocrystic olivine (as well as other mantle-, derived minerals—i.e. 1st Floor from the Mir kimberlite pipe in Yakutia, Russia. national Kimberlite Conference, Victoria, Canada. Locational and other information for the diamond deposits and kimberlites, lamproites, ultramafic lampropyhyres and garnet-peridotite facies alkali basalts Diavik pipe emplacements likely result from a shared five-stage emplacement continuum involving (1) exploitation of existing structures by early kimberlite magma intrusion, (2) initial pipe excavation, (3) pipe infilling, (4) sedimentation into craters, and (5) late magmatic intrusion. Total field magnetic contours for the C14 pipe, Kirkland Lake ..... 22 14. Photographs of drill core illustrating the overall macroscopic characteristics of the main varieties of volcaniclastic kimberlite observe, Ekati. Geochem-, suggest that the eruption process resulted in signifi-, cant loss of juvenile ash and preferential concentration, of the crystal component of the kimberlite (primarily, olivine). Our Kimberlite is guaranteed to be hand dug, unsearched, and come from real volcanic Kimberlite pipes in Colorado's Redfeather Lakes District! Geoscience Australia and state authorities. HK samples compared to PK samples, are attributed to the removal of these components in The internal HK and PK units also Lithos, 308, … geomagnetic relationship of Ekati’s economic kimberlites. Diamond distribution within the kimberlites reflects the amount and nature of mantle material sampled by individual kimberlite phases, but is modified considerably by eruption and depositional processes. Wood fragments are com-, mon and locally abundant. 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. These arrays correlate with decreasing olivine, of 1 or less. Long Abstracts, 8th Inter-. U, progressive break-up of an Archean superc. There are no differences in olivine composition between explosive (Grizzly) and hypabyssal (Koala) kimberlites. Samples from both internal HK units and PK units feature The, phases identified at Koala based on core and large-, diameter reverse circulation drilling include the fol-, black mudstone occurs in the uppermost portion of the. Some of the kimberlite pipes are very large producers. Kimberlite magmatism in the region occurred in different episodes over a long time scale. In addition, they appear to, display a stronger LREE enrichment (La/Yb>350), than that indicated by available data for Group 1 or, Group 2 kimberlites elsewhere (La/Yb typically, magmatic kimberlites fall within ranges published for, able data (Kjarsgaard per. There is a kimberlite pipe in Rockbridge County near Mt. Numerous Proterozoic diabase dykes intrude the area. sediment (quartz and mud) to very coarse-grained, olivine-rich VK at the base. In contrast, abundant Proceedings of the 7th International Kimberlite Conference. In: Gurney, B.H., et al. This may, later stage magmas responsible for the formation of, In certain cases, the kimberlite vents were filled or, volumes of MK. This texturally complex zone is interpreted to represent a clastogenic deposit formed by a low energy eruption within an open diatreme. Recent discoveries have been the pipes in North Canada, with Ekati now just starting production, and the Arklangelsk kimberlites in northern Russia. Jwaneng was, emplaced into competent Proterozoic lithologies, (platform sediments and minor mafic intrusives), overlain by an unknown thickness of unconsolidated, Observations made to date provide significant, constraints on the emplacement of the Ekati kimber-, lites and permit generalised models for how they, formed. Together, they provide seismic evidence for the trans-lithospheric nature of the Tintina Fault. Recent work on a satellite intrusion to the Misery, Main pipe suggests the presence of similar, but better. Resedimentation processes, were highly variable and likely included large-scale, collapse and mass-wasting of pyroclastic material into, the vent involving minimal reworking, talus slope, processes (e.g. Make your own jewelry, collect specimens, or explore our line of hand-crafted diamond ore jewelry, crystal ball spheres, polished slabs, and artisnal home furnishings. Exam-, ples are generally pale yellowish brown to grey, closely packed (generally clast supported) and com-, monly display well developed bedding on scales, ranging from metres to millimetres. Updated internal geological models feature two volcanic packages interpreted to represent two successive cycles of explosive eruption followed by active and passive sedimentation from a presumed crater-rim, both preceded and followed by intrusions of coherent kimberlite. Pipes dominated by magmatic kimberlite, Pipes entirely or partially filled by MK include, Leslie, Grizzly, Pigeon, Arnie and Mark. It is suggested that this required a sustained, high, energy eruption (or series of eruptions) that did not, involve significant interaction with wall rocks and, which is likely to have been driven primarily by, magmatic processes, i.e. However, the increased Al2O3 content in RVK is also positively correlated with Nb concentration indicating that the matrix consistently includes a small amount of kimberlitic ash. Bedrock and kimberlites are masked by tens of meters of wind-blown sand but when you put a magnetic image over the same area you can clearly see the kimberlite pipes hidden below that sand cover. However, mudstone xenoliths and disaggregated sediment, within the kimberlites indicate that late-Cretaceous and Tertiary cover (likely, emplacement. 1, Graham, I., Burgess, D., Bryan, D., Ravenscroft, P, Doyle, B.J., Hopkins, R., Armstrong, K.A., 1999. composition and melt evolution trajectories as a primary control on the explosive behaviour In diamonds the size and the quality of the stones is more important than the overall grade in terms of carats per hundred tons. facies of the south lobe, Jwaneng Mine, Botswana. However, it turns out that this is not true. Explosive devolatilisation of CO, -rich kimberlite magma is interpreted to have, been the dominant eruption mechanism, but phreatomagmatism is thought to have played a role and, in certain cases, may, The Ekati property is located in the central part of, the Slave Structural Province of the Canadian Shield, in the north-central and northeastern part of, the Lac de Gras map area (76D). Thus they reflect emplacement of kimberlite, The geological characteristics of kimberlites at, Ekati are broadly consistent with a two-stage em-, placement model involving pipe excavation followed, The presence of bedded RVK with incorporated, surficial material at depth and with low wall-rock, contents within the majority of pipes strongly suggests, that, at least in these cases, the pipe was excavated to, minimum depths of ca. Small clasts (mostly 0.5 to 2 mm) of fine-. Comparative geochemistry of kimberlites, from the Lac de Gras field, NWT—an integrated isotopic and, elemental study. The lack of an accompanying, equivalent increase in the concentration of either, are not related to dilution of juvenile kimberlitic, material by host rocks or surface sediments, elements that are depleted in PVK relative to MK, are primarily associated with the relatively late-stage, groundmass phases in kimberlite (i.e. Samples with low-Ti (and low, V) have lower total volatile content and lower CO, O ratios than those from the high-Ti group. first order transition elements by ICP-ES; all other elements by ICP-MS. the various Ekati magmatic kimberlites analysed, show broadly similar compositional features, certa, distinct differences are evident. Differences in the relative abundances of mantle minerals are shown among different pyroclastic domains in a single pipe, suggesting emplacement via multiple magma pulses containing unique mantle populations, while units from different pipes are, in some cases, more similar and re ect cross-fertilization among adjacent pipes. Microlitic diop-, side has not been observed. In Africa the big producers are Botswana, South Africa, Congo DRC, Angola and Namibia. The diffuse transitional zones exhibit intermediate compositions between cores and rims, attributed to partial re-equilibration of xenocrystic cores with the ascending kimberlite melt. by explosive exsolution of, Work undertaken to date on the Ekati kimberlites, clearly demonstrates that, while they display, morphological similarities to many southern African, kimberlites, they are occupied by distinctive volcani-, clastic lithologies that suggest formation by different, eruption and depositional processes. The presence of abundant, juvenile lapilli in the PVK suggests, however, that, magma was likely limited relative to earlier eruptions, that formed the olivine-rich VK deposits. 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. The Ekati kimberlites range in age from 45 to 75 Ma. The presence of smaller solid clasts, of fine-grained VK as well as mudstone xenoliths, and rare wood fragments within the upper TK also, this later eruption include the presence of diabase, dykes that may have structurally weakened the, wall-rock and/or weakening of the country rock by, conduits for groundwater and it is possible that, phreatomagmatism played a significant role in the, Fig. Three-dimensional models of selected Ekati kimberlites illustrating variation in pipe size and morphology. In contrast, internal zones form discrete layers with resorbed margins and restricted Mg# values, but variable Ni, Mn and Ca concentrations, which indicates a discrete crystallization event from precursor kimberlite melts at mantle depths. opening of a much larger vent, due to wall-rock instability/collapse may have. The VK units all, contain minor amounts of xenolithic shale and grano-, diorite that ranges in size from tens of centimetres to, typically occurs in low concentrations ( <, but breccia units (>15% country rock material) are, present in places. pipes, some of which may represent extrusive, The observed characteristics of the Ekati kimber-, lites are consistent with a two-stage eruption and, infilling process similar to that proposed by, volcanism is thought to have cleared the kimber-, lite vents and then built up a significant tephra cone, of highly fragmented, olivine-enriched juvenile ma-, terial with varying amounts of kimberlitic ash and, surface sediments (predominantly mud). 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. Kjarsgaard, B.A., Spark, R.N., Jacob, Z.J., 1994b. The dykes correspond to the MacKenzie and Lac, : This material is described in Section 5.5. Primary VK contains relatively minor. volcaniclastic kimberlite, whereas the Misery East pipe (7), East and Northeast extensions (9, 4) and Misery Mid-east dyke (6) are hypabyssal intrusions of magmatic kimberlite. The mine can be accessed from Butha-Buthe by a tar road which is approachable through a 5km-long gravel road. Drilling data suggest that below a, depth of ca. The latter include pipes infilled with steep, irregular VK blocks/wedges and at least one case in which the pipe is occupied by well-defined sub-horizontal VK phases, including a unique, 100-m-thick graded sequence. Pyroclastic and hypabyssal kimberlite units at Diavik exhibit subtle mineral The extent of Al-enrichment correlates with the proportion of dark, fine-grained clastic matrix material in the RVK samples and their composition can be explained as a mixture of a very olivine-rich, fines-depleted, juvenile component with varying amounts of argillaceous sediment likely derived from surface deposits present at the time of kimberlite eruption. mRVK, oVK, PVK, TK, MK), as well as differences in the proportions of specific, VK varieties and the geometry, size and spatial, relationships of kimberlite units present. ), Proceedings of the. Sandy VK samples, from the Koala kimberlite show similar trends to, observed in other VK samples but are considerably, quartz. olivine) material evident in most drill intersections. Groundmass spinel exhibits atoll-textures and is composed of a magnesian ulvöspinel – magnetite (MUM) or chromite core, surrounded by occasional pleonaste and a rim of Mg-Al-magnetite. This distinc-, tive style of volcanism is thought to stem from a, combination of geochemical (primarily volatile con-, tent) and near-surface geological factors. 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. Kimberlite and lamproite indercating stones found in southern western australia! and occupies a claim block of approximately, (see below). Location. 4 KIMBERLITIC SILLS, WESSELTON KIMBERLITE PIPE, SOUTH AFRICA.Figure 3. Rounded to, irregularly shaped clasts of fine-grained probable, primarily to the upper ca. The apparent continuity of this phase, across the pipe (present in all drill holes inte, the appropriate portion of the pipe) suggests that no, further eruptions occurred at Koala after deposition of, The transition from siltstone to the overlying, phase of graded mud-rich to olivine-rich RVK (Phase, 3) represents a substantial increase in the amount of, coarse-grained olivine being deposited. The low viscosity is likely responsible for non-explosive emplacement of the Benfontein sills, while the rhythmic layering is attributed to multiple magma injections. Wombat and Sue kimberlites), they dominate the, upper portions of the pipe. The graded beds (point 1 above), are interpreted to represent moderately olivine-rich, crater-rim material with intermixed (possibly inter-, bedded) mud and minor kimberlitic ash that slumped, into the excavated pipe and was deposited by sub-, aqueous debris flow processes involving varying, degrees of sorting. 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. tively coherent blocks into the Panda pipe. Because diamonds and kimberlite -- and other semi-precious gems -- are formed in similar locations, some kimberlite rock contains diamonds. The answer lies in the stone size and quality. A rock is designated as resedimented if there, is compelling evidence indicating that its pyroclastic, constituents have been moved (either en mass or in. Geology, Kjarsgaard, B.A., Spark, R.N., Jacob, Z.J., 1994a. MK occurs primarily as precursor dykes but, in a few cases, forms pipe-filling intrusions. The characteristics of the Ekati kimberlites are consistent with a two-stage emplacement process: (1) explosive eruption/s causing vent clearing followed by formation of a significant tephra rim/cone of highly fragmented, olivine-enriched juvenile material with varying amounts of kimberlitic ash and surface sediments (predominantly mud); and (2) infilling of the vent by direct deposition from the eruption column and/or resedimentation of crater rim materials. Soft sediment deforma-, tion features are commonly present. In contrast, the mRVK dominated units are characterised by a, massive, matrix-supported texture reflecting incorpo-, ration of significant amounts of surficial mud (, grained ash) and probable resedimentation into the, vent by debris flow processes. This juxtaposition of cold/hot and thick/thin lithosphere across a narrow transition zone has important implications for regional geodynamics. : +1-604-980-6771; fax: +1-604-980-6751. More detailed study is required to constrain models, 8.5. Deposition of PVK, possibly as within-vent py-, roclastic deposits formed by eruption column col-, lapse, generally occurred in the early stages of pipe, infilling, with intermittent eruptions causing inter-. Recent geological studies have recognised at least five distinct volcaniclastic lamproite lithofacies with differing diamond grades. They can then be obscured by soil, sediment, glacial till, and vegetation. Xenocrysts of mantle-derived gar-, net, pyroxene (chrome diopside and enstatite), chro-, Fig. (ca. 30 m) granodiorite boulders occur within the TK, phase, at a depth of approximately 80 m below the, base of the RVK phase and also in the lower part of, the mRVK phase on the northern side of the pipe. 5 to 30 m below the, contact with the overlying bedded mRVK phase. Kimberlite types include: mud-rich resedimented VK (mRVK); olivine-rich VK (oVK); sedimentary kimberlite; primary VK (PVK); tuffisitic kimberlite (TK) and magmatic kimberlite (MK). Observed variations in the bulk composition of coherent kimberlites correlate with their mode of emplacement and petrographic characteristics. Production output of the Prairie Creek Kimberlite Diamond Mine was considered to be small size. Kimberlite pipes in the Lac de Gras area have been shown to have been open holes during protracted periods of their development and, as such, to have acted as traps for deposits sourced from other nearby kimberlite eruptions, ... Early-stage kimberlite exploration is most commonly restricted to investigations of the uppermost depths of a given pipe (e.g., 50-200 m) due to costs of deeper exploration. Diamonds crystallize in the mantle well below the crust but they are carried up into the crust by the rising kimberlitic magma. The narrower rims are commonly overgrown by very, fine-grained microlitic clinopyroxene. Diamond grades of economic kimberlites vary hugely. The Precambrian rocks are overlain by Quaternary glacial sediments. Centimetre-scale bedding is mod-, erately developed in places but, in general, the mRVK, Dark brown to black fine-grained mudstone and, siltstone occur as rare blocks/bands ranging in thic, ness from tens of centimetres up to 5 m. The mor-, phology and lateral continuity of these intervals is not, constrained by the current drilling, however, expo-, sures in underground workings indicate that mudstone, occurs both as xenolithic blocks and as apparent in, situ lenses/bands. In particular, the data, indicate the presence of two broad groups, defined, also reflected in MgO concentrations and in terms of, their volatile contents. Bedded, olivine-rich VK is present to, depths of at least 430 m. Pit mapping and drill core, observations indicate that the VK units within Panda, are generally steeply dipping and not laterally or, vertically continuous. The P- and S-wave upper mantle structures of northwestern Canada reveal that the distribution of kimberlite fields in the Slave craton correlates with the margin of fast and slow seismic mantle anomalies, which could delineate weak zones in the lithosphere. Canadian Journal of Earth Sciences, Wright, K.J., 1999. 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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