Globe Progress Pit Closure Planning

摘要

OceanaGold Corporation's (OGC) Globe Mine is undertaking site closure. Globe Pit closure activitiesto date include sealing a historic adit, rehabilitation and revegetation of benches, and design of thepit lake spillway. The Globe Lake has been forming since the pit began to flood naturally inSeptember 2015, following the end of mining operations.The Globe orebody was mined historically as part of the Globe - Progress group of undergroundgold mines. An adit was intersected by the modern opencast operation. The adit is below the finallake level, which originally connected the underground mines to the nearby Devil's Creek. The aditwas sealed to prevent unplanned discharges as the lake filled. Sealing works included a concretetunnel plug, shotcrete and use of low permeable fill adjacent to seal fractured ground. A littoral zonewas incorporated above the sealing layer at the final lake level. The potential seepage pathways aremonitored.Early Globe Lake water quality monitoring identified high arsenic (As) concentrations as a risk toclosure objectives. OGC therefore adopted an adaptive management approach, involvingmonitoring total As stored in the Globe Lake water column. At Year 3 the monitoring and forecastedAs loads triggered 'in-pit ferric dosing'. This involves addition of ferric chloride to the Globe Laketo remove As from the water column by co-precipitation/adsorption.Arsenic load in the water column has decreased by over 80% following ferric dosing, enabling directdischarge of Globe Lake water to Devils Creek without further treatment. The lake level ismaintained by a syphon discharging offsite, while the Globe Spillway is constructed. The spillwayallows for the in-perpetuity discharge of Globe Lake to Devil's Creek.