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Photograph of drill core slabs of KIMB-1 (top two slabs) and KIMB-2 (bottom two slabs). Although both rock types are generally similar with respect to juvenile kimberlite components, KIMB-2 is characterised by a high proportion of mud in the interclast matrix and is thus brown in colour.
Source publication
The DO-18 and DO-27 kimberlites were discovered in 1993 in the Lac de Gras kimberlite province. The DO-18 kimberlite is located approximately 400 m north of DO-27 and is a separate, distinct body. The DO-18 kimberlite was emplaced into Archean granitoids of the Slave Province and an overlying veneer of late Cretaceous to Eocene mudstones. The pipe...
Contexts in source publication
Context 1
... logging and preliminary petrography has revealed the DO-18 body to be comprised of two main kimberlite domains. The largest of these is located primarily in the northern and central part of the body and is referred to as KIMB-1 ( Figure 2). KIMB-1 is characterised by a generally high proportion (> 25 %) of accessory country-rock granite and minor amounts of mud-rich resedimented volcaniclastic kimberlite (RVK). ...
Context 2
... second domain, referred to as KIMB-2 (Figure 2), is located primarily in the southern part of the body. KIMB-2 is a variably, but generally juvenile-rich, locally bedded, grey/brown kimberlite characterised by an inter-clast matrix dominated by mud and kimberlitic ash ( Figure 2). ...
Context 3
... second domain, referred to as KIMB-2 (Figure 2), is located primarily in the southern part of the body. KIMB-2 is a variably, but generally juvenile-rich, locally bedded, grey/brown kimberlite characterised by an inter-clast matrix dominated by mud and kimberlitic ash ( Figure 2). Accretionary lapilli comprising concentric rims of mud plus kimberlitic ash are locally present. ...
Citations
... The DO-18 kimberlite is a Group I kimberlite that is part of the Tli Kwi Cho kimberlite complex in the Lac de Gras kimberlite field of the Archaean Slave Craton in northern Canada ( Supplementary Fig. 4). It is a classic carrot-shaped kimberlite primarily composed of pyroclastic kimberlite (PK), with less dominant phases of re-sedimented volcaniclastic kimberlite (RVK), that intruded into undifferentiated Archaean granitoids [59][60][61] . Sedimentary mudstones and terrestrial palynomorphs that infill the kimberlite constrain the age emplacement to between 75 Ma and 45 Ma (Late Cretaceous to Eocene) at the northernmost stand of the Western Interior Seaway 61 . ...
... DO-18 is concealed by 5-20 m of glacial till ( Supplementary Fig. 3a) that was deposited during the most recent late Wisconsinan glaciation by westward flow (290-295°) 62,63 . The DO-18 kimberlite has an expression of 4 ha at the till-bedrock interface 61 . The Kelvin kimberlite is also hosted within the Slave Craton of northern Canada (Supplementary Fig. S3), as one of four gently dipping, irregular L-shaped pipes that make up the Kelvin-Faraday Corridor (KFC) cluster 64,65 . ...
Population growth and technological advancements are placing growing demand on mineral resources. New and innovative exploration technologies that improve detection of deeply buried mineralization and host rocks are required to meet these demands. Here we used diamondiferous kimberlite ore bodies as a test case and show that DNA amplicon sequencing of soil microbial communities resolves anomalies in microbial community composition and structure that reflect the surface expression of kimberlites buried under 10 s of meters of overburden. Indicator species derived from laboratory amendment experiments were employed in an exploration survey in which the species distributions effectively delineated the surface expression of buried kimberlites. Additional indicator species derived directly from field observations improved the blind discovery of kimberlites buried beneath similar overburden types. Application of DNA sequence-based analyses of soil microbial communities to mineral deposit exploration provides a powerful illustration of how genomics technologies can be leveraged in the discovery of critical new resources.
... The study area is located~30 km southeast of Lac de Gras and encompasses~110 km 2 , centred down paleo-ice-flow of the DO-18 and DO-27 kimberlite pipes (Fig. 1). The two kimberlites do have different origins, with DO-18 being a volcaniclastic kimberlite that is believed to result from a single extrusive event, while DO-27 is more complex, containing a mixture of pyroclastic, volcaniclastic and coherent kimberlite, with the surface expression dominated by pyroclastic kimberlite (Harder et al., 2008;Harder et al., 2009). Despite these differences, both pipes are characterized by a similar indicator mineral assemblage, dominated by garnets with less common occurrences of chrome diopside and chromite (Doyle et al., 1999;Harder et al., 2009). ...
Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n = 251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.
... The DO-27 kimberlite is located within the Lac de Gras province on the Slave Craton, Northwest Territories (NWT), Canada, that includes the EKATI™ and Diavik™ diamond mines (see Figure 1, Harder et al., 2008). The Lac de Gras kimberlites were emplaced into predominantly Archean granitoids of the Slave Province and an overlying veneer of late Cretaceous to Eocene mudstones (Doyle et al., 1999). ...
... The estimated grade of the DO-27 kimberlite based on Model 3 (1993-1994) was 1-36 cpht, which resulted in significantly decreased interest in the project. A revised geological model (Model 4, 1995) lead to a reevaluation of the kimberlite resulting in much improved estimated diamond grades of the volumetrically dominant kimberlite phase to approximately 90 cpht (Model 5, 2005-2008. Robust geological models, confirmed by numerous drill holes and interpreted in detail by an experienced geologist, are critical to accurate interpretations and ultimately the success of any kimberlite project. ...
This contribution reviews the evolution of geological models for the DO-27 kimberlite, located in the Lac de Gras kimberlite province, Northwest Territories, Canada. The DO-27 kimberlite was discovered as a geophysical anomaly in 1992, and early models of the kimberlite (Models 1–2) were based largely on geophysical surveys, with early core drilling confirming the presence of kimberlite. Core drilling completed in 1993 was used to create the first geological model, Model 3. Model 3 interpreted the dominant pipe infill to be ‘diatreme-facies’ kimberlite. Influencing the interpretation of Model 3 was the understanding of kimberlites at the time, which assumed most kimberlites were comparable to southern African-style kimberlites; these kimberlites were typically large, steep-sided bodies infilled by ‘diatreme-facies’ kimberlite. However, this was inconsistent with the much smaller kimberlites being discovered in the early 1990s in the Lac de Gras area. Bulk sample evaluation in 1994 was conducted based on the interpretation in Model 3, targeting the ‘diatreme-facies’ kimberlite. The resulting diamond grades were below expectations and the project was not evaluated further. However, several partners in the project questioned the validity of Model 3 and acquired a re-assessment of the same 1993 drill cores. The resulting geological model, Model 4, interpreted ‘pyroclastic kimberlite’ to be the dominant pipe infill; this pipe was located south of where the 1994 evaluation was focused. The ‘diatreme-facies’ kimberlite of Model 3 was reinterpreted to be low-volume intrusive sills, not infilling a pipe-like body. Based on this re-interpretation, DO-27 was re-evaluated from 2005–2007 by Peregrine Diamonds Ltd. through bulk sampling and core drilling. These new data were used to create Model 5, which builds on the interpretations of Model 4. Diamond grades obtained from the 2005–2007 bulk sampling were substantially higher than those from the 1994 evaluation, which has significant implications for the economic viability of the DO-27 kimberlite. The progression in understanding and geological modeling of DO-27 demonstrates the importance of reliable and accurate geological models in the economic assessment of kimberlite pipes.
... The DO-27 kimberlite is located within the Lac de Gras province on the Slave Craton, Northwest Territories (NWT), Canada, that includes the EKATI™ and Diavik™ diamond mines (see Figure 1, Harder et al., 2008). The Lac de Gras kimberlites were emplaced into predominantly Archean granitoids of the Slave Province and an overlying veneer of late Cretaceous to Eocene mudstones (Doyle et al., 1999). ...
... The estimated grade of the DO-27 kimberlite based on Model 3 (1993-1994) was 1-36 cpht, which resulted in significantly decreased interest in the project. A revised geological model (Model 4, 1995) lead to a reevaluation of the kimberlite resulting in much improved estimated diamond grades of the volumetrically dominant kimberlite phase to approximately 90 cpht (Model 5, 2005-2008. Robust geological models, confirmed by numerous drill holes and interpreted in detail by an experienced geologist, are critical to accurate interpretations and ultimately the success of any kimberlite project. ...
The DO-27 kimberlite is located within the Lac de Gras province on the Slave Craton, Northwest Territories (NWT), Canada, that includes the EKATI™ and Diavik™ diamond mines. The Lac de Gras kimberlites were emplaced into predominantly Archean granitoids of the Slave Province and an overlying veneer of late Cretaceous to Eocene mudstones. The DO-27 body is part of what was historically known as the Tli Kwi Cho complex, which was discovered in 1992, and has undergone a long history of exploration and evaluation by a number of operators. Evaluation of the kimberlite was conducted based on contrasting geological interpretations, which lead to significantly different estimations of the kimberlite area, volume and grade of kimberlite present. This contribution discusses the different geological models at various stages in the project history, the impact this had on the project, and the implications for evaluating other kimberlites.
The Tli Kwi Cho (TKC) kimberlite complex contains two pipes, named DO-27 and DO-18, which were discovered during the Canadian diamond exploration rush in the 1990s. The complex has been used as a testbed for ground and airborne geophysics and an abundance of data currently exists over the area. We provide historical and geologic background about the complex, the physical properties of interest for kimberlite exploration , and the geophysical surveys. We then carry out 3D inversion and joint interpretation of the potential field data. The magnetic data indicate high susceptibility at DO-18 and the magnetic inversion maps the horizontal extent of the pipe. DO-27 is more complicated. The northern part is highly magnetic and is contaminated with remanent magnetization; other parts of DO-27 have a low susceptibility. Low densities, obtained from the gravity and gravity gradiometry data, map the horizontal extents of both DO-27 and DO-18. We combine the 3D density contrast and susceptibility model into a single geologic model that identifies three distinct kimberlite rock units which agree with drilling data. In the two follow-up papers, our density and magnetic susceptibility models are combined with information from electromagnetic data to provide a multi-geophysical interpretation of the Tli Kwi Cho kimberlite complex.
The magnetic and electromagnetic responses from airborne systems at Tli Kwi Cho, a kimberlite complex in the Northwest Territories, Canada, have received considerable attention over the last two decades but a complete understanding of the causative physical properties is not yet at hand. Our analysis is distributed among three papers. In the first, we find a 3D magnetic susceptibility model for the area; in the second, we find a 3D conductivity model; and in the third paper, we find a 3D chargeability model. Our goal is to explain all the geophysical results within a geologic framework. In this first paper, we invert three independent airborne magnetic data sets flown over the Tli Kwi Cho kimberlite complex located in the Lac de Gras kimberlite field in Northwest Territories, Canada. The complex consists of two kimberlites known as DO-27 and DO-18. An initial airborne DIGHEM survey was flown in 1992 and AeroTEM and VTEM data subsequently acquired in 2003 and 2004, respectively. In this paper, we invert each magnetic data set in three dimensions. Both kimberlites are recovered in each model, with DO-27 as a more susceptible body than DO-18. Our goal is to simultaneously invert the three data sets to generate a single susceptibility model for Tli Kwi Cho. This project is part of a larger, on-going investigation by UBC-GIF on inverting magnetic, electromagnetic, and induced polarization data from the Tli Kwi Cho area.
