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(2020) Magnesium Isotope Signatures of Hydrotalcite Supergroup Minerals during Weathering and Carbonation of Ultramafic Mineral Wastes

Turvey C, Wilson S, Mavromatis V, Hamilton J, Dlugogorski B & Oskierski H


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12g: Room 4, Thursday 25th June 22:45 - 22:48

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Amy Lewis on Tuesday 23rd June 15:05
Hello there- nice presentation. I have a few questions! (1) I wondered how much CO2 is sequestered per year per tonne of waste material at these sites? (2) What sort of size the tailings on the whole? It seems in some of the images, some clasts are quite large (~5cm or similar), but I wondered if that was a typical size or the waste was varied in particle size. (3) Then, to assess the sample purity using XRD, was that based on quantitative whole rock XRD or was it done using another XRD application? Thank you!
Thanks for the questions. 1) The amount of CO2 sequestered varies across different sites from 200 - 2000 gCO2/m2/year, about 3 orders of magnitude higher than background weathering rates in Australia. At Mount Keith this results in 39800 t of CO2 per year, which is ~11% of mine emissions. 2) The grain size varies across different mine sites from <425 microns up to about 2cm for coarse waste, some of the larger clasts in the presentation are from waste rock rather than processed tailings. 3) We used qualitative XRD on the separated samples as we were just testing to see if we had pure hydrotalcite or if we had a another phase present.

Submitted by Elizabeth King on Thursday 25th June 17:08
From Conveners: 1) Is there a difference between pure and leached samples? Perhaps seeing an incomplete leaching effect? 2) Based on your work, do you still foresee potential in using Mg isotopes to track hydrotalcite mineral formation? Expanding from your last take home point, what specific information do you propose is still necessary to understand the preserved Mg isotope values of the hydrotalcites?
Thanks for the questions. 1) There does appear to be incomplete leaching for the pyroaurite (hydrotalcite) samples, as the residual serpentine does not have the expected serpentine composition. 2) If hydrotalcites exchange Mg with the local environment it would make it much harder to track hydrotalcite formation conditions. 3) Useful additional information would include tailings pore water and deeper unreacted samples that might preserve original Mg compositions.

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