The influence of volcanological and sedimentological processes on diamond grade distribution in kimberlites: examples from the EKATI Diamond Mine, NWT, Canada

Abstract

The distribution of diamonds within individual kimberlite pipes is poorly documented in the public domain due to the proprietary nature of the data. The study of the diamond distribution within two pipes, Fox and Koala, from the EKATI Diamond Mine, NWT, Canada, in conjunction with detailed facies models has shown several distinct relationships of deposit type and grade distribution. In both pipes, the lithological facies represent grade units which can be distinguished from each other in terms of relative size and abundance of diamonds. A positive relationship between olivine grain size and abundance with diamond size and abundance is observed, indicating that sorting of fragmental kimberlites influences diamond distribution. Though surface geological processes do not control the diamond potential of the erupting magma, they can be responsible for concentrating diamonds into economically significant proportions. A good understanding of the eruption, transport and depositional processes responsible for the individual lithological units and the diamond distribution within them is important for successful resource estimation. This may lead to recognition of areas suitable for selective mining, making a marginal deposit economic.

Alteration Styles in the Orion Central Volcanic Complex, Fort a la Corne Kimberlite Field, Saskatchewan, and Their Effects on Primary Volcaniclastic Textures: Implications for Facies Mapping and Diamond Exploration

“…Understanding the distribution of alteration zones has removed a level of complexity in determining the distribution of facies. Ultimately, as discussed above, olivine-size distributions are the best proxy for indicating diamond grade Scott Smith and Smith 2009;Porritt et al, 2011;Harvey et al, 2013). However, an improved knowledge of the facies distribution can assist in better targeted sampling strategies.…”

“…Diamonds, although proportionally minor, are primary depositional components of kimberlite deposits and the physical processes that control their size distribution and concentration are systematically related to those that affect the dominant olivine crystals Scott Smith and Smith, 2009;Porritt et al, 2011;Harvey et al, 2013). While the morphologies of primary olivine pseudomorphs are generally well-preserved, secondary alteration tends to mask the distribution of other primary components, in particular juvenile pyroclasts and interstitial matrix or pore space.…”

“…Olivine crystals are considered to be a semiquantitative proxy for diamonds, as both olivine and diamond have similar densities, and would thus have similar sorting and grain-size characteristics Scott Smith and Smith 2009;Porritt et al, 2011;Harvey et al, 2013). At the Orion Central volcanic complex, most coarse-grained olivines (>0.5 mm) are identifiable at least as altered pseudomorphs, thus quantitative methods for determining olivine crystal-size distributions in kimberlites, at least on a local sampling scale (e.g., Jerram et al, 2009;Moss et al, 2010;Harvey et al, 2013), can be applied here.…”

The influence of complex intra- and extra-vent processes on facies characteristics of the Koala Kimberlite, NWT, Canada: volcanology, sedimentology and intrusive processes

“…Information on the provenance of each kimberlite stratigraphic unit and lithofacies may have very important implications for understanding diamond grade variations in some pipes (e.g. Porritt et al 2011). …”

Volcanic Successions Associated with Ore Deposits

“…Porritt et al (2011) assessed the factors that influence diamond grades in the Ekati kimberlites of Canada. Many diamonds show signs of resorption, which affects their commercial value.…”