The Jacobina mining complex in northeastern Brazil consists of five underground mines - Canavieiras, João Belo, Morro do Cuscuz, Morro do Vento and Serra do Córrego.
The processing plant at Jacobina averaged approximately 7,500t/d in May, with an average of 7,200t/d for the entire June quarter. The company said this is a 5% increase over the production from the March quarter.
Yamana's Phase 2 expansion plans to increase the plant's processing rate by implementing incremental debottlenecking of the plant and tailings system, as well as operational improvements. The company expects this approach, which does not require the installation of an additional ball mill, to significantly reduce the project's CAPEX and improve energy efficiency, as well as de-risking the project.
In the March quarter, the company installed a new Falcon concentrator and cyclone bank at the plant, followed by an additional Knelson concentrator in the June quarter. It also increased the diameter of the pipeline that feeds the tailings storage facility (TSF) from 10in (25.4cm) to 16in (40.6cm), which relieved pipe pressures and increased design limits.
The team also modified the plant's operation to optimise the aperture of its crushers and the sizing of the screens, which reduced the feed size of the material entering the ball mills and resulted in improved milling performance. An increase in throughput while maintaining grinding size was also possible thanks to a new combination of mill liners and grinding balls.
In May and June, Yamana conducted trials at Jacobina to test the existing capacity of the processing plant and determine the optimal processing rate, as well as identifying any bottlenecks for future increases in throughput.
The trial conducted in May lasted six consecutive days, and the processing plant exceeded 8,000t/d while maintaining a gold recovery of over 96%, which is notably higher than the nameplate capacity. It achieved a maximum throughput of 8,176t/d.
In a further two-week trial in June, the plant exceeded 8,000t/d for 10 days with an average of 8,179t/d. The maximum throughput during this trial was 8,609t/d. Overall, throughput at the plant exceeded 8,000t/d for 21 days in the June quarter. The company stated that the trials demonstrate that the processing plant can consistently and reliably achieve a daily operating throughput above 8,000t/d.
However, following the trials, the plant processing rate is limited to a maximum monthly average of 7,500t/d, as defined by Yamana's operating permit for the Jacobina processing plant. The company is currently pending changes to the permit.
The Phase 2 expansion aims to increase throughput to 8,500t/d with a gold recovery of 96-97%, which would increase plant production to 230,000oz/y. Yamana stated that it is "confident that this objective can be achieved with its simplified approach to continue incremental debottlenecking and operational improvements without requiring an expansion of the grinding circuit as originally contemplated."
The company is considering post-commissioning operational adjustments to the Knelson and Falcon concentrators, as well as the potential to optimise the crushing circuit. There is also an opportunity to install fine screens to improve classification efficiency, which would prevent fine particles smaller than the target grind size from going back into the ball mills - this would allow mill capacity to be reserved for just the particles being reduced in size. The company plans to undertake test work in the September quarter to evaluate this opportunity.
To sustain the higher throughput rates, there will also need to be some minor upgrades to the backend of the processing plant and tailings pumping system. In line with the higher processing rate, production at the mine is also ramping up due to ventilation circuit improvements as well as more load and haul equipment being added to the fleet. The shotcreting work groups have also been optimised, which has reduced cycle times for development as well as providing access to further production zones.
Yamana expects that the CAPEX for the Phase 2 expansion will not exceed US$15-20 million, which is significantly lower than the original estimate from the project's pre-feasibility study. Subject to the successful completion of its permit modification, the company plans to start processing 8,500t/d by the second half of 2023. Operational data from the trials was used to adjust the processing model and set the baseline for any future expansions.
The company is also evaluating a potential Phase 3 expansion at Jacobina to increase throughput to 10,000t/d. The comprehensive plan would align the processing plant, underground mine, tailings strategy and permitting, and the engineering for Phase 3 would advance in parallel to Phase 2.
The company plans to complete a Phase 3 feasibility study in 2023, with project commissioning in 2027. One of the aspects being evaluated is the potential use of Rail-Veyor technology for ore haulage at the Canavieiras mine.
