Sunstone Metals Beats Scoping Study With 80% Copper and 93% Gold Recovery at Bramaderos
Key Takeaways
- New locked-cycle testwork at Bramaderos returned average copper recoveries of 80% and gold recoveries of 93%, beating the April 2026 Scoping Study assumptions of 75% and 85% respectively.
- Peak results were stronger still — up to 83% copper recovery into concentrates grading approximately 18% copper, with optimisation work pushing concentrate grades above 24% copper.
- Combined flotation and cyanidation delivered up to 94% overall gold recovery, with both the Brama Diorite (94%) and Brama Breccia (92%) lithologies responding well to conventional processing.
- Low arsenic content in the concentrates signals minimal smelter penalty risk, and offtake discussions have confirmed strong market demand and favourable pricing terms for Bramaderos concentrate.
- The improved recoveries will be incorporated into ongoing project studies, with El Palmar drilling expected to recommence in September 2026 and a revised NPV figure yet to be published.
Bramaderos metallurgical results lift recoveries above Scoping Study assumptions
New metallurgical test results from Sunstone Metals (ASX: STM) have returned copper and gold recoveries materially above the assumptions used in the April 2026 Scoping Study. The revised average recoveries of 80% for copper and 93% for gold compare favourably to Scoping Study assumptions of 75% copper and 85% gold, and are expected to have a material positive impact on the Bramaderos Project’s NPV, production, and unit costs.
The program was commissioned on the Brama-Alba-Melonal porphyry deposits at the Bramaderos Project in southern Ecuador. Testwork was undertaken at Intertek Kamloops and overseen by Pitchblack Group.
Patrick Duffy, Managing Director
“These are important results with highly favourable consequences for Bramaderos across all the key project metrics. 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.”
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What the test results actually showed
The locked-cycle flotation and cyanidation programs demonstrated that both principal ore types at Bramaderos, the Brama Diorite and Brama Breccia, respond well to conventional processing. Key outcomes from the testwork included:
- Locked-cycle flotation achieved copper recoveries of up to 83% into concentrates grading approximately 18% copper
- Optimisation work achieved concentrate grades exceeding 24% copper
- Combined flotation and cyanidation achieved overall gold recoveries of up to 94%
- Diorite lithology: flotation plus regrind and cyanidation delivered approximately 94% gold recovery
- Breccia lithology: approximately 92% gold recovery
- Low arsenic content indicates clean copper concentrates with minimal smelter penalty risk
Discussions with offtake providers confirmed Bramaderos concentrate would be in high demand and receive favourable pricing terms.
Recovery upgrade vs. Scoping Study at a glance
The table below summarises the revised recovery assumptions versus those used in the April 2026 Scoping Study. The revised figures apply assuming an 18% copper concentrate is produced.
| Metal | Scoping Study Recovery | Revised Recovery |
|---|---|---|
| Copper | 75% | 80% |
| Gold | 85% | 93% |
Understanding copper-gold metallurgy and why recovery rates matter
Metallurgical recovery rate is the percentage of metal contained in the ground that can actually be extracted and sold. The higher recoveries are expected to have a material positive impact on the project’s NPV, production, and AISC.
The conventional processing flowsheet at Bramaderos works in sequence. Ore is crushed and ground, then fed into flotation cells that capture copper-bearing minerals into a copper-gold concentrate. The leftover material, called flotation tails, is then treated with cyanidation to recover the remaining gold, producing gold doré. The combined process is what delivers both a copper-gold concentrate and a gold doré product from a single ore stream.
The announcement confirms the revised recoveries are expected to have a material positive impact on all three, though a revised NPV figure has not yet been quantified.
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What comes next for the Bramaderos Project
The metallurgical results now feed into ongoing project studies, with several near-term workstreams underway or planned:
- Further variability testing underway across additional ore domains
- Process optimisation parameters to be refined
- Process circuit trade-off studies (HPGR vs. SABC circuit options) to be completed
- Metallurgical results to be incorporated into process plant design and operating cost estimation for ongoing project studies
- El Palmar drilling expected to recommence September 2026
Bramaderos sits within a two-project Ecuadorian portfolio for Sunstone. The Bramaderos November 2025 Mineral Resource estimate stands at 220Mt at 0.50g/t AuEq for 3.6Moz AuEq, comprising 40Mt Indicated at 0.56g/t AuEq (0.6Moz) and 190Mt Inferred at 0.49g/t AuEq (2.9Moz). Beyond the resource, the project carries a Porphyry Exploration Target of between 4.1Moz and 11.2Moz AuEq within 315 to 505Mt, though the potential quantity and grade of exploration targets is conceptual in nature and it is uncertain whether further exploration will result in the estimation of a resource.
Managing Director Patrick Duffy framed the results within the company’s broader development strategy:
Patrick Duffy, Managing Director
“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.”
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