JOHANNESBURG (miningweekly.com) – Despite a number of unscheduled plant stoppages at its New Liberty gold mine, in Liberia, dual-listed Aureus Mining still processed 221 360 t of ore in the three months to September 30, at an average feed grade of 2.92 g/t, resulting in the production of 14 392 oz of gold.
In early May, Aureus temporarily suspended processing operations at the mine owing to problems with the detoxification circuit, which had not been operating to original design specifications. This resulted in higher concentrations of weak acid dissociated cyanide in the process effluent. The downtime has, since its restart in June, disrupted gold production.
However, Aureus noted that mining operations continued with 1.9-million tonnes mined, including 302 822 t of ore at an average grade of 2.61 g/t.
The mining operations mainly focused on the Kinjor stage 1 and 2 pits, opening access to fresh high-grade ore, with limited tonnage coming from the Larjor pit.
Grade control drilling continued throughout the three months under review, while a new drill rig had been delivered to site early this month to ensure that ore requirements early in the fourth quarter were met.
Plant optimisation and preventive maintenance activities also continued throughout the quarter, with the company's existing operations team being supplemented by MNG Gold's in-house expertise.
The process plant detoxification circuit was modified to recycle process plant effluent from the tailings storage facility (TSF) to reduce discharges from the TSF and changes were made to both the design and operation of the TSF, converting it from an open to a closed loop system with controlled discharges.
Throughout the third quarter, the process plant detoxification system has continued to operate to specification and all discharges into and out of the TSF have remained fully compliant with the company's environmental and operating permits.
Post the three months ended September 30, Aureus mined 1.05-million tonnes of material, representing a record tonnage of material moved in a month at New Liberty since mining operations started in 2015.
During October, the company produced 7 431 oz of gold. Mill use was 88% – the second consecutive month at this level. However, the gold recovery rate in October totalled 80%, which, while an improvement on the 72% achieved in September, remained below the design specification of 93% gold recovery.
Management believes the low gold recovery is primarily attributable to inadequate oxygen generating capacity of the existing process plant. Immediate action has been taken to address this, with orders having been placed for two additional oxygen plants, which are expected to be installed at site during the middle of the first quarter of 2017.
However, while recoveries remain low, management has decided to feed lower-grade ore through the plant to conserve the value of the higher-grade ore.
Management now expects fourth-quarter production to be in the range of 17 000 oz to 20 000 oz.