2017/2018 Season:

Date Speaker Talk Abstract
May 3, 2018 Curtis Brett, Senior Project Geoscientist, Rio Tinto Petrology of the White River Diamondiferous Paleoproterozoic Intrusive Rocks and Constraining the timing of the Destruction of the Southern Superior Cratonic Roots Diamond-bearing kimberlitic rocks have been identified as occurring within the Oskabukuta property,15km west of the town of White River, Northwestern Ontario. These rocks were emplaced within Neo-to-Mesoarchean (2.5 to 3.4 Ga) crystalline rock of the Wawa Subprovince, located within the Superior Province of North America. The emplacement age of the dyke is dated at 1945.3 ± 1.9 Ma (1σ) (U-Pb in perovskite). The diamond-bearing, kimberlitic intrusion has been mapped at surface for over a 900 m strike, and is referred to as the Rabbit Foot occurrence. Geothermobarometry of the nearby Proterozoic (2.7 Ga) aged diamondiferous metaconglomerate in Wawa (90 km SE) reported a maximum geothermal gradient range between 39 and 41 mW/m2 corresponding to a minimum lithospheric thickness of the Superior Craton of 190-220 km (Miller et al., 2012). In contrast, the study highlight that younger kimberlite (e.g. ~1.1 Ga Wawa kimberlite) within the Southern Superior record a substantially warmer conductive geotherm (46 mW/m2; Kaminsky et al., 2002) and maximum depth of garnet sampled of 150 km. Miller et al. (2012) interpret the apparent heating of the mantle is likely to have resulted from the Midcontinent Rift, which is broadly coeval with the Wawa kimberlite age. Pressure-Temperature estimates calculated using garnet and clinopyroxene xenocryst mineral compositions extracted from Rabbit Foot Model are consistent with model conductive heat flow of between 38-41 mW•m-2. These data support the interpretation of Miller et al. (2012) and further constrain the presence of a cool and thick Southern Superior keel at 1945 Ma. In fact, several of our garnet compositions support a minimum lithosphere-asthenosphere boundary of 250 km in depth and suggest (along with the presence of diamond) that the Rabbit Foot intrusion transected and sampled a significant portion of depleted and diamond stable lithospheric mantle at ~1945 Ma. A later thermal event, likely related to the Mid-continental rift, has subsequently heated and thinned the Southern Superior Craton, thereby constraining timing of the cessation of diamond fertile sublithospheric mantle in the region.
March 28, 2018 Dr. Yana Fedortchouk, Associate Professor, Department of Earth Sciences, Dalhousie University Dissolution features on diamond surfaces: What can they tell us? Link to Talk Video Diamonds are valued for their brilliance achieved by faceting of diamond crystals into the cut shapes that most efficiently reflect the light. However, diamond cut removes the long history of diamond growth and dissolution recorded in the surface features on rough diamonds. Growth features on diamond surfaces reflect the conditions of diamond-forming events in the mantle but are rarely preserved on natural diamonds due to their partial dissolution. The majority of natural diamonds show surface features resulted from dissolution both in the mantle source due to metasomatism and in the kimberlite magma during the ascent to the Earth’s surfaces. Mantle-derived resorption features can be preserved on diamonds enclosed in mantle xenoliths and protected from the interaction with the kimberlite magma during the ascent. The diamonds exposed to the reaction with the kimberlite magma develop kimberlite-induced dissolution features. This talk will discuss the large diversity of surface dissolution features on diamonds recovered from kimberlites. It will examine how the shape, size, and orientation of certain features can be used to deduce the conditions of kimberlite emplacement using the results of diamond dissolution experiments and observations on natural diamonds. The talk will discuss what we can learn about the behavior of volatiles and exsolution of fluid in kimberlite magma and how this supports or contradicts to what we know about kimberlitic fluid. The results of experiments conducted at mantle conditions are used to examine the kind of dissolution surfaces developed by diamonds during mantle metasomatism in fluids, in aqueous silicate melts and in carbonatitic melts. Comparison to the features of natural diamonds will assess what media dissolves diamond in the mantle, the prevalent diamond-destructive metasomatic agent, and will try to explain the repetitive cycles of growth and dissolution events recorded in single diamond crystals.
March 9, 2018 Tshireletso Dira and Dr. Leon Daniels, Pangolin Diamonds Corp Contrasting termite transported indicator mineral concentrations in the Kgalagadi of Central District Botswana: Macrotermes michaelseni vs Hodotermes mossambicus Link to Presentation Notes The Kalahari Formation desert sands covers most of the Karoo aged rocks in the Central District of Botswana which hosts the Orapa kimberlite field. The sole mechanism of transportation of kimberlite indicator minerals of post-Karoo kimberlites through the Kalahari Formation to the present day surface is through termite activity. If the termites are active in an area where a post-Karoo kimberlite is located, the termites will invariably transport indicators to surface. Indicators at surface are recovered from exploration soil samples. The dominant indicator transporter species of termites in the Orapa area is Macrotermes michaelseni. Their nests are characterised by large termite mounds at surface. A soil sampling programme sampling on a fixed grid basis over the eastern, unexposed part, of the BK11 kimberlite as well as termite hills on and off the kimberlite have confirmed that Macrotermes termites have the capacity to generate very high concentrations of indicators when the nest is directly over the kimberlite. Indicator counts from a standard sized soil sample can be in the thousands. Concentrations fall off rapidly as distance between the termite nest and kimberlite increases, indicating a limited area of influence. Individual nests may comprise up to 100 tonnes of material transported to surface. The Malatswae area is approximately 70 to 100 km southeast of the Orapa kimberlite field. The area is characterised by a scatter of kimberlitic garnets which indicate a very different mantle composition to the Orapa area, suggesting an undiscovered field of kimberlites. Concentrations of indicators in standard soil samples in the Malatswae area are in single digit levels. The dominant indicator transporter termite species in the Malatswae area is Hodotermes mossambicus. These termites construct their nests underground and discharge their “waste” through a wide distribution of vent holes. The volume of material discharged at a single vent hole is generally less than 200 ml, resulting in “background” counts of indicator concentrations. Current research into the relationship between dominant indicator transport termite species and indicator concentrations at surface have demonstrated that future exploration for kimberlites in Botswana (and elsewhere in Africa) will require an in depth knowledge of termite species as well as recognition of the earthmoving capabilities of the termite species in the area being explored.
February 7, 2018 Dr. Maya Kopylova, Professor, the University of British Columbia Inclusions in Cullinan diamonds: Insights on ancient hot spots and on the origin of Type II diamonds The talk will summarize three recent papers on mineral inclusions in 1.9 - 1.1 Ga diamonds from the Proterozoic Cullinan kimberlite (Kaapvaal craton, RSA). We studied 332 diamond inclusions from 202 Cullinan diamonds to investigate mantle thermal effects imposed by the formation of the Bushveld Igneous Complex. Diamonds indicate that the Proterozoic asthenosphere was hot, with Ts of 1450-1550°C, and upwelled from depths of at least 400 km, carrying unreverted dense minerals from the transition zone. The Cullinan diamonds may be unique on the global stage in containing a high proportion of inclusions equilibrated at temperatures exceeding the ambient 1327°C adiabat. The ability of diamonds to record super-adiabatic temperatures may relate to their entrainment from the deeper, hotter parts of the upper mantle un-sampled by the kimberlite in the form of xenoliths. For the Cullinan collection, we also compared mineral inclusions in nitrogen-free variety of diamond with those for the more common nitrogen-bearing diamonds. Both diamond types were sourced from the same three parageneses, lithospheric lherzolitic, lithospheric eclogitic, and sublithospheric mafic. The similarity of the mineral parageneses and C isotopic compositions in the Cullinan Type II and Type I diamonds indicate the absence of distinct mantle processes or the distinct carbon source for formation of Type II stones. The parent rocks and the carbon sources for Type II diamonds vary within a kimberlite and between kimberlites.
Nov 7, 2017 Branko Deljanin, CGL-GRS Swiss Canadian Gemlab Diamond Fluorescence: Its Effect on the Diamond Pricing and the Use of Fluorescence for Diamond Identification This hands-on workshop will start with a brief introduction of the history of a marketing plot that lowered prices on fluorescent diamonds in the 70s. At present, the discount on the price of the fluorescent diamonds can be as severe as 50%. Currently there are efforts challenging the justification for these discounts, based on reviews of the diamond appearance in different lighting environments. The workshop will continue with a demonstration of diamond fluorescence using an extensive diamond collection. Diamond fluorescence is seen in all colour hues, in a wide range of intensities and is different under short-wave and long-wave UV. Additionally, the phenomenon of phosphoresence, a longer light emittance than fluorescence, can be observed with some diamond types. These colourful luminescent glows can reveal information about the natural or synthetic origin of a diamond and the diamond treatment. The workshop will demonstrate the new portable equipment to examine diamond fluorescence on small (melee) and larger rough and polished diamonds and will discuss how the equipment aids in identification of natural and synthetic stones.
Oct 17, 2017 Dr. Wayne Barnett, Principal Structural Geologist, SRK Consulting Kelvin and Faraday Kimberlite Emplacement Geometries and Implications for Subterranean Magmatic Processes The Kennady North Project, owned by Kennady Diamonds, is located approximately 280 kilometers east-northeast of Yellowknife. The kimberlite bodies are named Kelvin, Faraday 1, Faraday 2 and Faraday 3, and have complex geometries atypical of the more common subvertical kimberlite pipes. Rather, these pipe-like bodies are inclined between 12 and 30 degrees towards the northwest. On-going detailed petrographic studies have shown that the pipes contain layers of complex volcaniclastic units with variable volumes of xenolithic fragments, as well as coherent magmatic layers. The pipe textures include evidence for high energy magma and country rock fragmentation processes typically observed in open volcanic systems. We conclude that the pipe development geometry and process is governed by a combination of stress, structure and magmatic fluids. These pipes are creating new questions about kimberlite emplacement processes and exploration target models that are fascinating to explore.

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Past meetings 2012/2014 Season

Past meetings 2018/2019 Season