Sunstone Metals Limited has lifted average metallurgical recoveries at the Bramaderos gold-copper project in southern Ecuador to 80% for copper and 93% for gold following a comprehensive test work program.

The updated figures exceed the recovery assumptions used in the April Scoping Study, which assumed 75% recovery for copper and 85% for gold. Sunstone retracted that study in May following consultation with the ASX regarding the proportion of inferred resources in the initial production target. The company subsequently commenced optioneering studies and metallurgical test work to support ongoing project evaluation.

Testing overseen by Pitchblack Group at Intertek Kamloops evaluated the principal Brama-Alba lithologies, confirming that conventional flotation can be applied effectively to both the Brama Diorite and Brama Breccia mineralisation. Locked-cycle flotation trials achieved copper recoveries of up to 83% into concentrates grading approximately 18% copper. Low arsenic levels in the material indicate potential to produce clean copper concentrates with minimal smelter penalty risk.

The test work also established that combining flotation with cyanidation of flotation tails can achieve overall gold recoveries of up to 94% for the diorite lithology and 92% for the breccia. The process flowsheet incorporates crushing, grinding, flotation, and cyanidation of flotation tails to yield a copper-gold concentrate and gold dore.

“The increased recoveries are very positive for the forecast Bramaderos production and NPVs and lower unit costs significantly in the process. Essentially, the key to this breakthrough lies in the fact that the locked-cycle testwork has confirmed the technical viability of conventional flotation processing for Bramaderos.”

“Both the copper and gold recoveries are materially higher than the assumptions used in the April 2026 Scoping Study and consistent with our strategy to progressively grow the value of the overall Bramaderos Gold-Copper Project. These outcomes provide a robust metallurgical foundation for the ongoing project studies and support the continued advancement of Bramaderos as a potential large-scale gold-copper development opportunity.”

— Patrick Duffy, Managing Director

The revised recovery assumptions will serve as the basis for future gold equivalent calculations and project studies. Sunstone is undertaking further metallurgical variability testing and process circuit trade-off studies, with an updated Mineral Resource estimate scheduled for release in the December quarter of 2026.

Read the full announcement: Metallurgical tests deliver increased Bramaderos recoveries