Browsing by Author "Poitras, J"

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    The critical role of bacteria in mineral carbonation of kimberlite
    (Goldschmidt, 2022-07-12) Jones, TR; Poitras, J; Senzani, K; Ndlovu, S; Vietti, A; Paterson, DJ; Wilson, SA; Southam, G
    The breakdown of ultramafic rock during natural weathering captures carbon dioxide from the atmosphere to form carbonate minerals. Kimberlite, an ultramafic rock that can produce diamond weathers when exposed to water. These water-rock interactions also contribute to the growth of bacteria, which accelerate the weathering process. Yellow ground (oxidized Kimberlite found at the surface) samples from the South African Voorspoed and Kareevlei mines contained both molecular signatures (16SrDNA) and viable bacteria. Our molecular analyses highlighted a bacterial population consistent with serpentinite soils and demonstrated that bacteria play a role in yellow ground formation. These yellow ground cultures can grow using only kimberlite as a substrate, promoting weathering in order to live, and providing cultures that are important to natural weathering, yellow ground formation and subsequent mineral carbonation. In order to demonstrate the importance of biology in mineral carbonation of kimberlite, we performed X-Ray Fluorescent Microscopy (XFM) at the Australian Synchrotron to obtain structural and compositional analysis of the South African Venetia mine’s massive volcaniclastic kimberlite (MVK) Coarse Residue Deposit (CRD) with and without biofilm (weathering), 50-year-old Cullinan CRD and definitive, friable Kareevlei yellow ground. These analyses demonstrated that calcium, potassium and iron can be used as tracers for weathering and mineral carbonation. Our small laboratory and larger (1000 L) field-based mineral carbonation experiments both demonstrated the importance of photosynthetic biofilms in the carbonation of kimberlite residue. All of our experiments produced intergranular cements, which stabilised the CRD residue, providing a strategy to increase mine safety while sequestering carbon. We observed continued mineral carbonation with depth demonstrating that carbonation will continue as the kimberlite is buried on the mine site, which will achieve even greater carbon offsets than anticipated. Our pilot scale field experiment demonstrated that we offset 20% (on a mass equivalent) of the annual mine emissions in one year using bacterial carbonation, with the likelihood of continued carbonation ensuring that we will have the capacity to produce a carbon neutral mine.
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    Historical diamond mine waste reveals carbon sequestration resource in kimberlite residue
    (Elsevier, 2023-02) Jones, TR; Poitras, J; Paterson, DJ; Southam, G
    Mined sub-aerially stored kimberlite provided a natural laboratory in which to examine the potential for carbon sequestration in ultramafic materials. A 15 cm hand sample of ∼50-year-old ‘cemented’ coarse residue deposit (CRD) collected from a cemented surface layer in the Cullinan Diamond Mine tailings in Gauteng, South Africa, demonstrated the encouraging effects of weathering on mineral carbonation of kimberlite. The examination of petrographic sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron – energy dispersive spectroscopy demonstrated that weathering produced extensive, secondary Ca/Mg carbonates that acted as an inter-granular cement, increasing the competency of the CRD, i.e., producing a hand sample. Nearly every grain in the sample, including primary, un-weathered angular carbonate clasts were coated in secondary, μm- to mm-scale carbonate layers, which are interpreted as secondary materials. DNA analysis of an internal, aseptic sample of secondary carbonate revealed that the weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation that was found within the secondary carbonate, interpreted as a biomaterial. The formation of secondary carbonate demonstrates that ‘waste kimberlite’ from diamond mining can serve as a resource for carbon sequestration. © 2022 Elsevier B.V.
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    Transition metal mobility and recoverability from weathered serpentinite and serpentinite skarn tailings from Lord Brassey Mine, Australia and Record Ridge, British Columbia, Canada
    (Goldschmidt, 2022-07-14) Honda-McNeil, M; Wilson, SA; Locock, A; Mililli, B; Zeyen, N; Wang, B; Turvey, C; Vessey, CJ; Patel, AS; Hamilton, JL; Southam, G; Poitras, J; Jones, TR; Jowitt, S; Lowock, A
    As mineral resources become scarcer, companies are lowering their ore cut-off grades and resorting to exploring deeper underground and in more isolated areas. Incorporating tailings storage facilities and tailings reprocessing as part of the ore processing circuit can potentially extend the lives of mines and save on future exploration costs. Ultramafic and mafic mine tailings host resources including first and second row transition metals, such as nickel (Ni), cobalt (Co), and platinum group elements (PGE), whose high value and recovery could serve as a motivator for existing mines to reprocess their tailings. Many of these target metals are initially hosted by olivine, are repartitioned during serpentinization to form sulfides, oxides and alloys, and then are remobilized during weathering to form authigenic carbonates, sulfates and oxyhydroxides. Reprocessing tailings may further provide environmental benefits, including a reduction in waste output and the ability to offset greenhouse gas emissions by enhanced silicate-weathering and carbonation reactions. Here we use powder X-ray diffraction, scanning electron microscopy, electron probe micro-analysis and synchrotron X-ray fluorescence mapping to demonstrate how first and second row transition metals are mobilized to their final sinks. Samples of serpentinite, skarn and weathered tailings from the historical Lord Brassey nickel mine in Tasmania, Australia and weathered outcrops of serpentinite ore from the proposed magnesium mine in Record Ridge, BC, Canada are analyzed and compared. Preliminary results from these climatically similar localities indicate clear transition metal dissemination patterns across alteration zones and distinct partitioning behavior (ex. homogenous distribution of Ni within sulfides) in weathering products. By developing an understanding of the sinks for metals across the mining lifecycle, we aim to cultivate an economically.