Sunstone Metals Boosts Bramaderos Project Value with Higher Copper and Gold Recoveries

Metallurgical Breakthrough Raises Project Economics

Sunstone Metals (ASX:STM) has delivered a significant boost to the economics of its Bramaderos Gold-Copper Project in southern Ecuador, unveiling metallurgical test results that show copper recoveries climbing to 80% and gold recoveries reaching 93%. These figures surpass the April 2026 Scoping Study assumptions of 75% and 85%, respectively, suggesting a material uplift in project net present value (NPV), production volumes, and all-in sustaining costs (AISC).

The company attributes this improvement to successful locked-cycle flotation tests confirming that conventional flotation can effectively process both principal ore types, Brama Diorite and Brama Breccia. Copper concentrates grading approximately 18% copper with low arsenic content were produced, reducing smelter penalty risks and enhancing concentrate marketability.

Detailed Testwork Validates Processing Approach

Extensive metallurgical work, conducted at Intertek Kamloops and overseen by Pitchblack Group, assessed ore hardness, mineralogy, flotation response, and recovery potential. The results revealed that both Diorite and Breccia samples contain abundant pyrite and chalcopyrite, typical of copper-gold porphyry deposits. Liberation analysis indicated that fine grinding below 38 microns is necessary to optimise chalcopyrite recovery.

Comminution tests classified the ores as moderately hard but with favourable crushing and abrasion characteristics, supporting the use of a conventional SAG-ball mill circuit. Locked-cycle flotation trials achieved copper recoveries up to 83% and gold recoveries up to 57% into concentrates with grades of 17-18% copper and 33-48 g/t gold. Further optimisation improved concentrate grades beyond 24% copper.

Complementing flotation, cyanidation of flotation tails boosted overall gold recoveries to about 94% for Diorite and 92% for Breccia, underpinning a flowsheet combining flotation, regrinding, and cyanidation to maximise metal extraction.

Project Advancement and Exploration Targets

Sunstone’s Managing Director Patrick Duffy highlighted the importance of these results in underpinning the technical and economic viability of Bramaderos as a large-scale development opportunity. The improved recoveries provide a robust foundation for ongoing engineering studies, including process plant design and operating cost estimation.

Meanwhile, Sunstone continues to expand its resource base with ongoing drilling campaigns. The company has recently reported extensive mineralised intersections at the Porotillo prospect, which lies outside the current 3.6 million ounce resource and is expected to contribute to an upcoming resource update this December. This drilling progress aligns with the company’s strategy to grow Bramaderos’ footprint and value.

In addition to Bramaderos, Sunstone’s El Palmar Project in northern Ecuador holds a 1.2 million ounce gold equivalent resource and hosts significant exploration targets. Drilling is slated to recommence there in September 2026, pending funding.

Next Steps Focus on Optimisation and Drilling

Further variability testing is underway to refine metallurgical parameters and validate performance across additional ore domains. Trade-off studies comparing different processing circuits are planned to optimise plant design. Concurrently, Sunstone aims to advance drilling programs at key exploration targets such as Melonal, Limon, Copete, and Porotillo, subject to funding availability.

These developments position Bramaderos as a compelling copper-gold project with improved recoveries that could translate into stronger project economics and lower costs, while the broader Ecuador portfolio offers multi-decade growth potential.