2021 Annual Report

Cemented paste backfill (paste fill or paste) is used at Nova to fill the open underground voids after the ore from each stope is mined. This provides support for the overlying rock and allows complete extraction of the orebody. The Nova paste backfill plant takes the wet tails slurry from the Nova processing plant after the valuable minerals are extracted. Cementitious binder material is mixed in, and the resultant paste is piped underground into the mined voids where it cures into a solid block. During the annual update of the Life of Mine (LOM) schedule in 2020 it was identified that paste backfill production rate was a potential mining process bottleneck that, if improved, would allow a more consistent grade and mine production profile and yield large benefits to the project Net Present Value (NPV). The Nova paste backfill plant at the time was running at design nameplate capacity of 30,000- 35,000m³ of paste fill per month. The optimum rate was determined to be 45,000m³ per month, with an initial target of 40,000m³ established. The project ‘Paste 45k’ was born. A cross functional team was assembled, comprising of mining, metallurgy, engineering and maintenance representatives, guided by the Nova business improvement team. The task was to identify areas of opportunity and use a business improvement methodology to understand and ultimately make improvements to the most valuable areas. Operations Broadly the improvements fell into three categories: increasing plant throughput, increasing plant availability/reliability, and reducing operational delays. By design, the Nova paste plant was configured to use only the non-sulphide tailings stream, of which the majority was already being used. Test work was completed which showed that a percentage of the sulphide tails stream could be added into the mix without compromising the strength of the final product. This additional material enabled a significant improvement to the throughput volume. Analysis of plant downtime identified an array of opportunities in preventative maintenance and reliability. Notably, improvements were made to the maintenance strategy and, in some cases, design changes to the major components such as the paste mixer, binder augers and conveyors. A concerted effort was made to efficiently utilise the planned mill outages and any opportune outages to conduct maintenance and improvement activities. Reductions in operational delays have centred around scheduling to ensure that multiple fill sites are always available and enhanced by enabling quick changing between fill sites through the installation of efficient mechanical pipe switching equipment underground. To date, the project has yielded an improvement of over 20%, exceeding the 40,000m³ target and reliably achieving 45,000m³ per month when required. The resultant rates were included in the FY22 LOM plan with a significant improvement in the LOM mine profile. Case Study: Nova Paste Backfill Improvement Nova’s Operations Team 18 — IGO ANNUAL REPORT 2021