Brightstar Resources says laboratory testwork across deposits representing about 80% of its Sandstone resource supports a conventional gravity and carbon-in-leach processing route, with average recoveries around 94%. The results provide the processing basis for the project’s pre-feasibility study, although Bull Oak and further variability testing remain outstanding.
- 93.7% weighted recovery across 51 optimised tests at 24 hours
- 95.7% average CIL recovery across 13 master composites
- Gravity recovery averaged 41.7% across master composites
- Five million tonne per annum plant design basis established
- Bull Oak testwork and maiden Ore Reserve still pending
Brightstar Resources Limited (ASX:BTR) has cleared one of the more consequential technical hurdles at its Sandstone Gold Project, with interim metallurgical results supporting a conventional processing plant and average gold recoveries of about 94%. The result gives the company a workable flowsheet for the project’s December-quarter pre-feasibility study, rather than forcing it towards a more exotic or technically demanding treatment route.
Recovery results cover most of Sandstone’s resource
The 51 optimised tests produced a weighted average overall recovery of 93.7% at 24 hours and 94.4% at 48 hours. Across 13 master composites, average direct-leach recovery reached 94.6%, while carbon-in-leach, or CIL, testing averaged 95.7%, with results ranging from 89.7% to 99.3%.
The samples came from nine deposit groups representing approximately 80% of Sandstone’s 2.9 million-ounce Mineral Resource, which stands at 69.3 million tonnes grading 1.3 grams per tonne gold. Deposit-level results were generally strong but not uniform: 24-hour recovery ranges included 92% to 97% at Two Mile Hill, 90% to 99% at Montague-Boulder, 90% to 98% at Whistler and 86% to 99% at Indomitable. Achilles recorded the widest stated range, at 73% to 95%.
Gravity gold and rapid leaching support conventional design
Gravity recovery averaged 41.7% across the master composites, with individual results ranging from 11.1% to 68.9%. Two Mile Hill, Whistler and Achilles each produced master-composite gravity recoveries above 66%, while the testwork indicated that the gravity response was more closely linked to the orebody than to the oxide, transitional or fresh weathering categories.
The balance of the gold leached quickly, with around 90% of the gold recovered within the first eight hours in the program described by Brightstar. The results support a 24-hour leach residence time and a flowsheet built around primary crushing, SABC grinding to a P80 of 75 microns, gravity recovery and CIL.
PFS plant design moves to five million tonnes a year
GR Engineering Services has completed PFS-level engineering for a five million tonne per annum CIL facility, including preliminary plant design and capital and operating cost estimates. Comminution testing across 50 composites produced what Brightstar describes as a conservative design basis for ore hardness and abrasiveness, with final mill sizing still being refined against the planned mine schedule and ore blend.
The processing case is also helped by low reagent requirements. Sodium cyanide consumption averaged 0.23 kilograms per tonne across the 13 master composites, while most tests required no lime to maintain the target pH. The company reported no preg-robbing or refractory characteristics, although elevated arsenic at Havilah and tellurium and bismuth at Montague-Boulder will require further assessment during the definitive feasibility stage.
Bull Oak remains the important unfinished test
The encouraging result is not yet a complete project-wide metallurgical picture. Bull Oak, a 10.5 million-tonne resource containing 322,000 ounces, remains under test, alongside additional variability composites, further work on an Achilles transitional sample and final comminution modelling. Brightstar says Bull Oak is expected to show characteristics comparable with Two Mile Hill, but that expectation is not a substitute for the outstanding laboratory results.
The Sandstone PFS remains scheduled for the December 2026 quarter, alongside an updated Mineral Resource and maiden Ore Reserve. The testwork provides a stronger technical foundation for those studies, but the next important question is whether the recovery assumptions and preliminary plant estimates survive the transition from laboratory composites to a mine schedule and, ultimately, full-scale operating conditions.
Bottom Line?
The metallurgy supports a relatively straightforward Sandstone development case, but the PFS still needs to convert strong laboratory recoveries into credible plant costs, mine scheduling and an Ore Reserve.
Questions in the middle?
- Will Bull Oak deliver recoveries consistent with the tested deposits once its leach work is complete?
- How will the Havilah arsenic and Montague-Boulder tellurium and bismuth results affect final process design and operating costs?
- What capital and operating cost assumptions will GR Engineering Services attach to the five million tonne per annum plant in the PFS?