St Barbara Ltd says that results of the current testwork program have allowed the early selection of the Saleable Concentrate Flowsheet option for the Simberi Sulphides Expansion, three months ahead of schedule. The expansion project has the potential to extend the life of mine by at least 10 years. The Simberi Operations consist of an open pit gold mine and processing plant on the northernmost island in the Tabar group of islands in the province of New Ireland in Papua New Guinea.
The testwork program has also confirmed that the Sorowar ore has significantly lower competency than previous test results, reducing the average life of mine (LOM) ore competency by 20% thereby reducing the crushing and grinding energy requirements.
Managing Director and CEO Andrew Strelein said: “We are excited by the improvements in the recoveries-to- concentrate and overall recovery being achieved in the flotation testwork we have completed to date. The results have allowed us to take an early decision in favour of the Saleable Concentrate Flowsheet, three months earlier than anticipated.”
He adds: “The confirmation of our expectations of the consistency and competency of the Sorowar ore’s crushing and grinding characteristics with those of Simberi’s other ore zones is a breakthrough. The simplification of the ROM pad and crushing circuit was just the first ‘value-unlock’ that we anticipate from this important clarification of the Sorowar ore properties. The testwork program is revealing enormous potential for flexibility in the sequencing of the open pits, pit backfill strategies to reduce waste dump construction and potential savings in waste haulage costs as well as dramatically simplifying mine closure and reclamation planning.”
Strelein continues: “The demonstrated benefit of the flotation circuit design optimisation and the value we have unlocked from confirming Sorowar’s ore properties have already delivered a return on our investment in FY24’s comprehensive metallurgical drilling and testwork campaign.”
The company says it is well funded to complete the next phases of work and beyond, including the investment in Pre- Expansion Growth Capital. This sets it up to deliver the clearest possible scope of work for the final investment decision anticipated in Q2 December FY26.
With comminution testwork now complete, preliminary comminution modelling of the LOM ore blend has confirmed the crushing and grinding circuit configuration and major equipment sizing. Crushing will be via a new MMD 625 Series Sizer. This has recently been purchased.
The existing 2.6 MW SAG mill is being retained and will be coupled with a new 5 MW ball mill. The ball mill size is based on a preliminary grind size selection of 106 μm as it showed an improved recovery, grade and concentrate mass pull over the previously selected grind size of 150 μm. Further grind size versus recovery testwork is planned and an economic assessment of the final optimum grind size will be made when testwork is complete.
The circuit design that includes retention of the existing SAG mill will minimise downtime related to tie-in of the new circuit. The current Carbon-in-Leach plant has parallel, rather than sequential, SAG and ball milling circuits allowing the SAG mill to continue operating while the new ball mill is installed. The circuit design will also be configured to allow rapid changeover between oxide/transitional ore processing (direct leach) and sulphide ores (flotation and leach).
Cyclone overflow from the new ball mill circuit will be pumped to a new flotation circuit. Flotation circuit configuration and equipment selection will reflect the testwork objectives of maximising flotation gold recovery as the tailings leach recoveries are relatively low (<50%); and producing a concentrate with a gold grade suitable for sale.
Flotation tails streams will be combined and leached in the existing leach/Carbon-in-Leach circuit. Testwork to date suggests that the leach stage will add approximately 6% to the overall recovery, which justifies its continuing operation for the treatment of the flotation tails. The gold recovered in the leach circuit is much lower than for the current operation and therefore the existing gold recovery circuit will not require upgrading.
As previously outlined in its 10 Year Plus Outlook for Simberi, St Barbara has committed to funding some of the Sulphide Expansion activities ahead of the formal investment decision. These investments support the improved performance/reliability of the current operations and/or removes the complexity and improves the timing of the future construction timeline (eg camp upgrades and process plant structural refurbishment).
Two low hour Volvo A60H trucks were purchased for trialling to confirm performance and cost parameters following the Mine Fleet Selection trade-off study that was conducted late last year. These trucks were identified in the study as being one of the preferred options as they provide a combination of higher capacity than the current small articulated trucks (CAT 740 / 745, Terex TA400 and Rokbak RA40s), whilst maintaining a narrower width and better manoeuvrability than larger rigid body alternatives such as the CAT 777, which is well suited to narrower cutbacks on the smaller pits. These trucks are now in service and are contributing to the current mining operations.
The semi-mobile Sizer unit has been ordered from MMD to replace the current feeder-breaker that feeds the Aerial Rope Conveyor (RopeCon). The Sizer will be utilised over the next few years, in a skid-mounted configuration, to provide greater crushing capacity and improved product size on the more competent ore that is being exposed in the deeper parts of the Sorowar orebody. This will improve the RopeCon availability and present a finer feed size to the milling circuit. The Sizer has been selected to meet the Sulphides Expansion duty specification and will be relocated to its permanent installation at the process plant when the RopeCon is decommissioned. The RopeCon will be replaced by a shorter dedicated haul road to a new run-of-mine (ROM) pad at the Process Plant as part of the Sulphides Expansion.
For FY25 the mine plan has been adjusted to deliver a softer blend to the existing feeder-breaker before commissioning the new Sizer in Q3 March FY25. This will minimise the impact of harder ores on the availability of the RopeCon until the Sizer is commissioned. The RopeCon belt is also being replaced in September 2024, which will also provide additional service life and reliability for the remaining years of oxide processing.
