Carbon dioxide (CO(2)) 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 its the hydrated magnesium carbonate minerals nesquehonite [MgCO(3)center dot 3H(2)O], dypingite [Mg(5)(CO(3))(4) (OH)(2)center dot 5H(2)O], hydromagnesite [Mg(5)(CO(3))(4)(OH)(2)center dot 4H(2)O], and less commonly lansfordite [MgCO(3)center dot 5H(2)O]. Textural relationships suggest that carbonate precipitates formed in situ after milling and deposition of tailings. Samples of efflorescent nesquehonite are characterized by delta(13)C values between 6.52 and 14.36 per mil, delta(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 CO(2) during mineralization. Samples of dypingite +/- hydromagnesite collected front within 0.2 m of the tailings surface give delta(13)C values between -1.51 and +10.02 per mil, delta(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 CO(2) in a soil-like environment.