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Abstract

Economic incentives for reducing industrial greenhouse gas emissions have emerged, including carbon tax and voluntary markets for carbon offset credits. Minor amounts (~1-3 wt.%) of brucite [Mg(OH)₂] in mine tailings from nickel and diamond mines offer a potentially energy-efficient pathway for offsetting greenhouse gas emissions from mining. This is because brucite naturally reacts with atmospheric CO₂ at significant rates to form carbonate minerals, and therefore energy-intensive technologies are not required to force carbon sequestration reactions to take place. Existing technologies can monitor and quantify the amount of CO₂ that has been sequestered in mine tailings. The baseline rate of sequestration is ~2,400 t CO₂ per km² of partially saturated and brucite-bearing tailings. This can amount to a ~10% offset (~40,000 t CO₂ per year) for select mines such as Mount Keith that have exceptionally large tailings storage facilities that are not covered by water. However, the percentage of ore that contains brucite may be low for most nickel and diamond deposits, and the presence of 1-3 wt.% brucite is likely to be unreported by conventional workflows. Here, new workflows are developed to identify brucite-bearing ore types from preexisting whole-rock geochemistry and short-wave infrared data that are often routinely collected on exploration drill core and blastholes for other purposes. The focus of this methodology development is resolving the problems of non-unique mass balance solutions, spectral feature overlap, low analyte concentrations, and sparse/expensive training data. For mines where the brucite-bearing ore types are rare, these workflows could help maximize CO₂ sequestration by delineating the brucite-bearing ore so it can be processed through the Mill immediately before rotating to a different tailings discharge spigot. Thus, a consistent rate of atmospheric CO₂ capture could be achieved by depositing a thin layer of brucite-bearing tailings on top of a thick layer of brucite-barren tailings before rotating spigots. Concurrent research has also made progress on engineering systems for flue gas injection into brucite-bearing media and has shown that tilling brucite-bearing tailings may double the CO₂ flux. These developing technologies may increase the CO₂ capture capacity of brucite-bearing tailings if their life cycle analyses prove favorable.