Carbon Dioxide Fixation within Mine Wastes of Ultramafic-Hosted Ore Deposits: Examples from the Clinton Creek and Cassiar Chrysotile Deposits, Canada

Abstract

Carbon dioxide (CO2) is sequestered through the weathering and subsequent mineralization of the chrysotile mine tailings at Clinton Creek, Yukon Territory, and Cassiar, British Columbia, Canada. Accelerated weathering is attributed to a dramatic increase in surface area, which occurs during the milling of ore. We provide a detailed account of the natural process of carbon trapping and storage as it occurs at Clinton Creek and Cassiar, including mineralogy, modes of occurrence, methods of formation for carbonate alteration, light stable isotope geochemistry, and radiocarbon analysis. Powder X-ray diffraction data were used to identify weathering products as the hydrated magnesium carbonate minerals nesquehonite, and less commonly lansfordite [MgCO3⋅5H2O]. Textural relationships suggest that carbonate precipitates formed in situ after milling and deposition of tailings. Samples of efflorescent nesquehonite are characterized by δ 13 C values between 6.52 and 14.36 per mil, δ 18 O values between 20.93 and 26.62 per mil, and F 14 C values (fraction of modern carbon) between 1.072 and 1.114, values which are consistent with temperature-dependent fractionation of modern atmospheric CO2 during mineralization. Samples of dypingite ± hydromagnesite collected from within 0.2 m of the tailings surface give δ 13 C values between -1.51 and +10.02 per mil, δ 18 O values between +17.53 and +28.40 per mil, and F 14 C values between 1.026 and 1.146, which suggests precipitation from modern atmospheric CO2 in a soil-like environment. Field observations and isotopic data suggest that hydrated magnesium carbonate minerals formed in two environments. Nesquehonite formed in an evaporative environment on the surface of tailings piles, and dypingite and hydromagnesite formed in the subsurface environment with characteristics similar to soil carbonate. In both cases, these minerals †

Determining timescales of natural carbonation of peridotite in the Samail Ophiolite, Sultanate of Oman

“…In addition, both subaerial and seafloor ultramafic rocks are known to take up significant CO 2 in secondary alteration minerals (e.g. ; ; Trommsdorff and Evans, 1977;Trommsdorff et al, 1980;Ferry, 1995;Surour and Arafa, 1997;Kelley et al, 2001;Fr h-Green et al, 2003;Ludwig et al, 2006;2011;Wilson et al, 2006Wilson et al, , 2009aWilson et al, , 2009b; ; . Therefore, even though ultramafic rocks are less abundant than other types of silicate rocks on Earth's surface, the influence of ultramafic rocks on the carbon cycle may nonetheless be important.…”

“…Brenker et al, 2007;Dasgupta and Hirschmann, 2010) while only a few studies have investigated rates of CO 2 uptake during weathering of ultramafic rocks (e.g. Wilson et al, 2006Wilson et al, , 2009aWilson et al, , 2009b. Wilson et al (2006Wilson et al ( , 2009aWilson et al ( , 2009b) investigated active carbonation of kimberlite diamond mine tailings in northern Canada and demonstrated that these mine tailings sequester on the order of 106 kg C0 2 /yr for each mine.…”

“…Wilson et al, 2006Wilson et al, , 2009aWilson et al, , 2009b. Wilson et al (2006Wilson et al ( , 2009aWilson et al ( , 2009b) investigated active carbonation of kimberlite diamond mine tailings in northern Canada and demonstrated that these mine tailings sequester on the order of 106 kg C0 2 /yr for each mine. The amount of CO 2 sequestered annually in kimberlite mine tailings is small relative to -35 x 1012 kg of anthropogenic CO 2 emitted in 2010 (Friedlingstein et al, 2010).…”

The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites

“…Wilson et al (2009) offsetting some of the greenhouse gas emissions associated with mining activities. The nature of the host species that bind carbon crystallographically was critical for assessing the amount of stored CO 2 in that study, since gangue minerals (e.g., magnesite) and surface precipitates (e.g., hydromagnesite) play different roles and must be distinguished.…”

“…Conversely, the exchange of Cl for CO 3 could fix in excess of 40 000 metric tons CO 2 per year, if end-member iowaite is reacted to form pyaroaurite. Total greenhouse gas emissions at Mount Keith are approximately 350 000 metric tons CO 2 equivalent (Wilson et al 2009). Careful stewardship of anion exchange reactions in hydrotalcite group minerals could, thus, substantially impact the greenhouse gas emissions of mine operations.…”