Brightstar Resources Confirms 94% Gold Recovery Across Sandstone’s 2.9Moz Resource

94% average gold recovery confirmed across Sandstone’s 2.9Moz resource

Metallurgical testwork for the Sandstone Pre-Feasibility Study (PFS) has returned average gold recoveries of 94% across deposits representing approximately 80% of the 2.9Moz Sandstone Mineral Resource. Every deposit tested has been confirmed as amenable to a conventional gravity and CIL flowsheet, a result that directly de-risks the processing case ahead of the PFS.

Brightstar Resources has engaged GR Engineering Services Limited to prepare PFS-level designs and costings for a 5 million tonne per annum (Mtpa) CIL processing facility on this basis. The Sandstone PFS remains on track for delivery in the December quarter 2026 (DecQ’26), alongside the next Mineral Resource update and maiden Ore Reserve.

What the testwork found — recovery, gravity and leach performance

High recoveries across every deposit tested

The testwork program covered nine deposits across all three weathering domains: oxide, transitional and fresh. Per-deposit recovery ranges at 24 hours, drawn from both master and variability composites, are as follows:

• Two Mile Hill: 92%–97%
• Montague-Boulder: 90%–99%
• Whistler: 90%–98%
• Indomitable: 86%–99%
• Musketeer: 94%–99%
• Vanguard: 90%–99%
• Achilles: 73%–95%

The 51-test program average (master and variability composites combined) returned an overall gold recovery of 93.7% at 24 hours, as reported in Figure 3 of the announcement. The 13 master composites alone averaged 94.6% overall direct-leach recovery and 95.7% CIL recovery at 24 hours.

Gravity gold — a cost advantage built into the ore

Master composites averaged 41.7% gravity recovery across the program, with individual composites reaching as high as 71%. The standout results were Two Mile Hill fresh MC2 (68.9%), Whistler fresh (66.1%) and Achilles fresh (66.0%).

Gravity recovery captures a portion of gold before chemical leaching begins, which reduces both processing cost and reagent demand. The remaining gold after gravity concentration leaches rapidly: approximately 90% is recovered within the first 8 hours, and the 24-hour leach residence time has been confirmed as the PFS design basis. The 48-hour results showed only a modest uplift over 24 hours, reinforcing this design choice.

Low reagent consumption and clean ore chemistry

Sodium cyanide (NaCN) consumption remained low across the program at the optimised conditions of 300ppm initial and 200ppm maintained NaCN. Lime demand was negligible: the majority of composites required no lime addition to maintain the target pH range using site water, and the maximum lime consumption in any optimised test was 0.5kg/t.

No preg-robbing, refractory characteristics, or deleterious elements were identified at any deposit. Two minor flags were noted: elevated tellurium and bismuth at Montague-Boulder, and elevated arsenic at Havilah (arsenic at 741ppm in the Havilah fresh master composite). Both have been flagged for further assessment during the Definitive Feasibility Study (DFS) and are not considered PFS blockers.

Managing Director Alex Rovira

“These are outstanding results and exactly what we expected Sandstone would be. Every deposit tested is amenable to a conventional gravity and carbon-in-leach flowsheet, the average recovery across the program is 94%, and the gravity recoverable gold component is high, which bodes well for both recovery and processing cost…”

All figures sourced from Table 3 and Table 4 of the ASX announcement dated 24 September 2026. Recovery ranges reflect both master and variability composites at optimised 24-hour leach conditions.

What is a CIL processing circuit — and why does it matter here?

A gravity and carbon-in-leach (CIL) circuit is a two-stage gold processing approach. First, gravity concentrators (in this case, a Knelson concentrator) capture free or coarse gold from the crushed and ground ore — no chemicals required at this stage, just centrifugal force. The remaining material is then finely ground and leached with a dilute cyanide solution. Gold dissolves into the solution and is adsorbed onto activated carbon, which is later processed to recover the gold metal.

This is considered a conventional processing route. The alternatives — refractory processing, pressure oxidation (POX), or bioleach — are significantly more complex and expensive, typically required when gold is physically locked inside sulphide minerals and cannot be accessed by cyanide leaching alone. The Sandstone testwork has confirmed that none of these more intensive approaches are needed.

The commercial significance of high gravity recovery is straightforward. Gravity is cheap and fast: capturing 42% of gold on average before the leach stage lowers cyanide and reagent consumption, and reduces operating costs. Combined with Sandstone’s rapid leach kinetics (approximately 90% of remaining gold recovered within the first 8 hours) and low reagent demand, the overall processing cost profile for the project is expected to be favourable. These characteristics feed directly into the capital and operating cost estimates GR Engineering Services Limited is preparing for the PFS financial model.

Why this matters — the path to a December quarter PFS

Processing flowsheet now locked in

The metallurgical program has confirmed the processing flowsheet for the Sandstone PFS: conventional primary crush, SABC (SAG mill, ball mill and pebble crusher) grinding circuit to a target grind of P80 75µm (the size at which 80% of particles pass a 75 micrometre screen), gravity recovery, and a 24-hour CIL circuit.

GR Engineering Services Limited has completed PFS-level engineering for the preliminary plant layout and has prepared the associated capital and operating cost estimates for the 5Mtpa facility. CMW Geosciences has completed PFS-level tailings storage facility layout options. A preliminary EPC (engineering, procurement and construction) implementation schedule has also been developed, covering early engineering, long-lead equipment procurement, construction and commissioning.

Remaining work and December quarter delivery

A defined set of testwork remains outstanding before the PFS is finalised:

• Bull Oak leach testwork (in progress; given similar geology and quartz-veining to Two Mile Hill, comparable outcomes are expected)
• CIL testwork on additional variability composites
• Further assessment of the Achilles transitional composite
• Additional variability composites
• Comminution circuit modelling using the PFS mine schedule and life-of-mine ore blend to confirm mill sizing

The Sandstone PFS remains on track for delivery in DecQ’26, in parallel with the next Sandstone Mineral Resource update and the declaration of a maiden Ore Reserve. That combination represents a significant cluster of value catalysts arriving in a single quarter.

Sandstone in context — part of a 4.5Moz company

Sandstone sits within a broader portfolio that gives Brightstar Resources considerable scale. The company holds 4.5Moz of total Mineral Resources across its Goldfields and Sandstone regions, both located in Western Australia.

The Goldfields Project is already in construction, with a 1.5Mtpa processing plant underway and gold production targeted to commence in JunQ’CY27 at a rate of more than 75koz per annum for six years. The January 2026 updated Feasibility Study for Goldfields outlined an A$606 million NPV8, a 74% internal rate of return, and approximately A$1 billion in life-of-mine cash flows. The Sandstone PFS represents the next major value inflection point for the company, with the processing case now firmly de-risked by the testwork reported here.

For investors exploring how the Sandstone PFS fits into the company’s broader production ambitions, our dedicated guide to Brightstar’s 200,000oz production roadmap covers the sequencing of Goldfields and Sandstone milestones and the capital allocation strategy behind the combined target.

The Goldfields Feasibility Study outlined an A$606 million NPV8 and approximately A$1 billion in life-of-mine cash flows, providing a comparable template for the financial framework GR Engineering Services Limited is now assembling for the Sandstone PFS.

Ready to Explore Brightstar’s Sandstone PFS in More Detail?

Metallurgical testwork has confirmed 94% average gold recovery across deposits representing approximately 80% of Sandstone’s 2.9Moz resource, with every deposit amenable to a low-cost conventional gravity and CIL flowsheet — a result that materially de-risks the processing case ahead of the December quarter 2026 PFS delivery.

With GR Engineering Services Limited now preparing capital and operating cost estimates for the 5Mtpa facility, the Sandstone PFS represents a significant value catalyst sitting alongside Brightstar’s Goldfields construction programme. Visit the Brightstar Resources investor profile on Discovery Alert to track the company’s progress across its 4.5Moz portfolio and understand how Sandstone fits into the broader 200,000oz production roadmap.