Abstract:

At the currently closed Troilus Gold-Copper Mine Site, many decades of pre-mining, intra-mining, and post-mining Acid Rock Drainage (ARD) studies have predicted widespread ARD at the site using standard predictive criteria. Yet decades later, limited ARD can only be found on a small scale at Troilus. To investigate this, many integrated studies included: (1) full-scale on-site monitoring; (2) large on-site kinetic tests of various rock units; (3) static testing of carefully selected core intervals based on sulphur geostatistics, dominant rock units, and 3D spatial distributions; (4) dozens of various laboratory kinetic tests; (5) mineralogy using four closely integrated methods; (6) rates of both sulphide oxidation and CO₂ capture using special enclosed chambers and humidity cells; (7) compilations of published silicate-mineral stoichiometry, neutralization capacities, and reaction rates; and (8) a literature review.

These integrated studies revealed several important aspects of Silicate Neutralization Potential (NP). These include: (1) only a small portion of the silicate minerals reacts sufficiently fast to neutralize fully; (2) the calcium-rich plagioclase minerals of bytownite and labradorite were most important; (3) microscale pH around plagioclase minerals can be important for predicting ARD; (4) at slower rates of acid generation such as from coarser particles, additional silicate minerals can contribute significant Effective NP; and (5) at faster rates of acid generation that create lower microscale pH levels, neutralization by other silicate minerals can accelerate and contribute significant Effective NP.

General geochemical analyses like four-acid-digestion ICP-MS of Troilus samples can be mathematically adjusted to estimate Fast-Neutralizing Silicate NP. This allows the ~158,000 drill core assays at Troilus to become more reliable surrogate acid-base accounts (ABAs).

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Maude Lévesque Michaud