A Mg Isotopic Perspective on the Mobility of Magnesium During Serpentinization and Carbonation of the Oman Ophiolite

Obeso, Juan Carlos de; Ramos, D. P. Santiago; Higgins, John A.; Kelemen, P. B.

doi:10.1029/2020jb020237

Cited by 19 publications

(11 citation statements)

References 84 publications

(266 reference statements)

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“…This is consistent with simple isotope mass balance considerations that dictate that Mg isotopes are not fractionated during complete dissolution of minerals, such as expected for weathering of magnesite or brucite (Mumpton and Thompson, 1966;Moore et al, 2017). Accordingly, measurable suggest that some of the above alteration products can form at near-ambient temperatures (De Obeso et al, 2020;Streit et al, 2012).…”

Section: Mg Isotopic Constraints On Weatheringsupporting

confidence: 82%

“…Consequently, brucite is often considered as the primary source of Mg during natural carbonation of mine tailings and it has been linked to increases in pore water pH, carbonation rate and yield, as well as the CO2 storage capacity of tailings in laboratory carbonation experiments (Pronost et al, 2011;Harrison et al, 2013;Assima et al, 2014;Boschi et al, 2017) and in Canada (δ 26 Mg = -2.50 ‰, ± 0.69 ‰ (2σ), n=4, magnesite rich sediments in Mavromatis et al, 2021). The extreme depletion of 26 Mg in this type of magnesite has been ascribed to magnesite dissolution/re-precipitation and the associated Mg isotope fractionation between Mg species in alkaline solutions and to concurrent precipitation of serpentine veins with high δ 26 Mg (Oskierski et al, 2019;De Obeso et al, 2020).…”

Section: Sources Of Mg In the Tailingsmentioning

confidence: 99%

“…Micro-analysis of Mg isotopic compositions is developed for carbonates (e.g.Traces of magnesite in the tailings and magnesite nodules in the mine pit atWoodsreef indicate limited, low temperature carbonation of the ultramafic bedrock prior to mining(Oskierski et al, 2013b;. The δ 26 Mg of nodular magnesite at Woodsreef (δ 26 Mg = -3.26 ‰, ± 0.10 ‰), is consistent with that of similar occurrences of low-temperature, ultramafic-hosted magnesite in the GSB (δ 26 Mg = -2.73 ‰, ± 0.76 ‰ (2σ), n=4,Oskierski et al, 2019), in Austria (δ 26 Mg = -2.36 ‰, ± 0.71 ‰ (2σ), n=7, Kraubath-type magnesite inEbner et al, 2019), in Oman (δ 26 Mg = -3.34 ‰, ± 0.20 ‰ (2σ), n=6, DeObeso et al, 2020)…”

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confidence: 99%

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Mineralisation of atmospheric CO2 in hydromagnesite in ultramafic mine tailings – Insights from Mg isotopes

Oskierski

Turvey

Wilson

et al. 2021

Geochimica et Cosmochimica Acta

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In this study we present the first Mg isotope data that record the fate of Mg during mineralisation of atmospheric CO2 in ultramafic mine tailings. At the Woodsreef Asbestos Mine, New South Wales, Australia, weathering of ultramafic mine waste sequesters significant amounts of CO2 in hydromagnesite [Mg5(CO3)4(OH)2•4H2O]. Mineralisation of CO2 in above-ground, sub-aerially stored tailings is driven by the infiltration of rainwater dissolving Mg from bedrock minerals present in the tailings. Hydromagnesite, forming on the surface of the tailings, has lower δ 26 Mg (δ 26 MgHmgs = -1.48 ± 0.02 ‰) than the serpentinised harzburgite bedrock (δ 26 MgSerpentinite = -0.10 ± 0.06 ‰), the bulk tailings (δ 26 MgBulk tailings = -0.29 ± 0.03 ‰) and weathered tailings containing authigenic clay minerals (δ 26 MgWeathered tailings = +0.28 ± 0.06 ‰). Dripwater (δ 26 MgDripwater = -1.79 ± 0.02 ‰) and co-existing hydromagnesite (δ 26 MgHmgs = -2.01 ± 0.09 ‰), forming in a tunnel within the tailings, and nodular bedrock magnesite [MgCO3] (δ 26 MgMgs = -3.26 ± 0.10 ‰) have lower δ 26 Mg than surficial fluid (δ 26 Mg = -0.36 ‰) and hydromagnesite. Complete dissolution of source minerals, or formation of Mg-poor products during weathering, is expected to transfer Mg into solution without significant alteration of the Mg isotopic composition. Aqueous geochemical data and modelling of saturation indices, along with Rayleigh distillation and mixing calculations, indicate that the 26 Mg-depletion in the drip water, relative to surficial water, is the result of brucite dissolution and/or precipitation of secondary Mg-bearing silicates and cannot be assigned to bedrock magnesite dissolution. Our results show that the main mineral sources of Mg in the tailings (silicate, oxide/hydroxide and carbonate minerals) are isotopically distinct and that the Mg isotopic composition of fluids and thus of the precipitating hydromagnesite reflects both isotopic composition of source minerals and precipitation of Mg-rich secondary phases. The consistent enrichment and depletion of 26 Mg in secondary silicates and carbonates, respectively, underpins the use of the presented hydromagnesite and fluid Mg isotopic compositions as a tracer of Mg sources and pathways during CO2 mineralisation in ultramafic rocks.

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Section: Mg Isotopic Constraints On Weatheringsupporting

confidence: 82%

Section: Sources Of Mg In the Tailingsmentioning

confidence: 99%

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confidence: 99%

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Mineralisation of atmospheric CO2 in hydromagnesite in ultramafic mine tailings – Insights from Mg isotopes

Oskierski

Turvey

Wilson

et al. 2021

Geochimica et Cosmochimica Acta

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“…The switch from isochemical reaction (except for the addition of water) to open system conditions generally induces a decrease in the MgO/SiO2 ratio of the serpentinised peridotites by several percents (Snow and Dick, 1995;Niu, 2004;Malvoisin, 2015). This decrease could be associated with Si gain (Malvoisin, 2015;de Obeso and Kelemen, 2018;Templeton and Ellison, 2020) and/or Mg loss (Snow and Dick, 1995;de Obeso and Kelemen, 2020;de Obeso et al, 2021). Si-rich fluids can be formed during orthopyroxene serpentinisation (Beard et al, 2009;Frost et al, 2013) or mafic rock alteration (Bach et al, 2004;Paulick et al, 2006).…”

Section: Implication For Post-serpentinisation Alterationmentioning

confidence: 99%

Nanostructure of serpentinisation products: Importance for water transport and low-temperature alteration

Malvoisin

Auzende

Kelemen

2021

Earth and Planetary Science Letters

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“…Listvenite is the end result of carbonation of a peridotite, where all Mg resides in carbonate minerals (magnesite ± dolomite) and Si is in quartz, usually with green chromian mica (muscovite-fuchsite solid solution and/or relict Cr-rich spinel; Halls & Zhao, 1995). Listvenite at and near this locality has been the subject of many studies (de Obeso et al, 2021;Falk & Kelemen, 2015;Nasir et al, 2007;Stanger, 1985;Wilde et al, 2002) and was sampled in rock core from Oman Drilling Project (OmanDP) Hole BT1B (Beinlich et al, 2020;Kelemen, Matter. et al, 2020;Menzel et al, 2020).…”

Section: Listvenite Field Sitementioning

confidence: 99%

Tracing Carbonate Formation, Serpentinization, and Biological Materials With Micro‐/Meso‐Scale Infrared Imaging Spectroscopy in a Mars Analog System, Samail Ophiolite, Oman

Leask

Ehlmann

Greenberger

et al. 2021

Earth and Space Science

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Visible-shortwave infrared (VSWIR) imaging spectrometers map composition remotely with spatial context, typically at many meters-scale from orbital and airborne data. Here, we evaluate VSWIR imaging spectroscopy capabilities at centimeters to sub-millimeter scale at the Samail Ophiolite, Oman, where mafic and ultramafic lithologies and their alteration products, including serpentine and carbonates, are exposed in a semi-arid environment, analogous to similar mineral associations observed from Mars orbit that will be explored by the Mars-2020 rover. At outcrop and hand specimen scales, VSWIR spectroscopy (a) identifies cross-cutting veins of calcite, dolomite, magnesite, serpentine, and chlorite that record pathways and time-order of multiple alteration events of changing fluid composition; (b) detects small-scale, partially altered remnant pyroxenes and localized epidote and prehnite that indicate protolith composition and temperatures and pressures of multiple generations of faulting and alteration, respectively; and (c) discriminates between spectrally similar carbonate and serpentine phases and carbonate solid solutions. In natural magnesite veins, minor amounts of ferrous iron can appear similar to olivine's strong 1-μm absorption, though no olivine is present. We also find that mineral identification for carbonate and serpentine in mixtures with each other is strongly scale-and texture-dependent; ∼40 area% dolomite in mm-scale veins at one serpentinite outcrop and ∼18 area% serpentine in a calciterich travertine outcrop are not discriminated until spatial scales of <∼1-2 cm/pixel. We found biological materials, for example bacterial mats versus vascular plants, are differentiated using wavelengths <1 μm while shortwave infrared wavelengths >1 μm are required to identify most organic materials and distinguish most mineral phases.

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A Mg Isotopic Perspective on the Mobility of Magnesium During Serpentinization and Carbonation of the Oman Ophiolite

Cited by 19 publications

References 84 publications

Mineralisation of atmospheric CO2 in hydromagnesite in ultramafic mine tailings – Insights from Mg isotopes

Mineralisation of atmospheric CO2 in hydromagnesite in ultramafic mine tailings – Insights from Mg isotopes

Nanostructure of serpentinisation products: Importance for water transport and low-temperature alteration

Tracing Carbonate Formation, Serpentinization, and Biological Materials With Micro‐/Meso‐Scale Infrared Imaging Spectroscopy in a Mars Analog System, Samail Ophiolite, Oman

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