Mine Water Quality Predictions for Permitting and Engineering Design at an Underground Gold Mine

摘要

An unnamed gold mine received water rights and a water dischargepermit after extensive environmental and engineering studies and achallenging permitting process. Ore will be mined using undergroundmining methods, which will encounter a number of differentlithologies, containing 2% sulphide (on average) as pyrrhotite, withminor occurrences of pyrite, arsenopyrite and chalcopyrite. The long-term acid generation potential and corresponding mine water qualityoriginating from the development rock is of paramount interest, as aportion of the underground mine workings will be exposed above thepost-closure water table. Multiple levels of conservatism were incorporated into the waterquality prediction effort. In addition to standard kinetic tests, net acidgeneration (NAG) testing was conducted to confirm "terminal" acidgeneration potential and metal leaching potential. The geological-geochemical block model that formed the basis of the water qualitypredictions assigned a reactivity classification to each rock type basedon the results of acid base accounting; long-term reactivity wassubsequently confirmed by kinetic testing and NAG testing. Thetransparent, conservative conceptual approach to mine water qualitypredictions ensured development and implementation of protectiveengineering design and long-term rock management strategies.Operational and post-closure water quality predictions were used todevelop operational management strategies to prevent and mitigate theonset of acid generation and metal leaching, including the developmentof operational waste rock segregation criteria, beneficial use of marble,targeted backfill of reactive rock below the final water table, andshotcreting of exposed reactive mine wall.