Sunstone Metals Lifts Gold Recovery to 93% Boosting NPV at 3.6Moz Ecuador Project
Key Takeaways
- Sunstone Metals has upgraded Bramaderos gold recovery to 93% (from 85%) and copper recovery to 80% (from 75%), with management confirming a material positive impact on NPV, production forecasts, and unit costs across the 3.6Moz AuEq resource.
- Locked-cycle flotation testwork at Intertek Kamloops confirmed a conventional processing flowsheet — crushing, grinding, flotation, and cyanidation of flotation tails — achieving up to 94% combined gold recovery for the Diorite ore type.
- Concentrate grades exceeding 24% copper are achievable through further optimisation, and low arsenic content has been confirmed, with offtake providers already indicating high demand and favourable pricing terms for Bramaderos concentrate.
- The updated 80% copper and 93% gold recovery assumptions will now be applied to all future AuEq calculations, directly feeding into ongoing project studies including process plant design and operating cost estimation.
- Bramaderos carries a porphyry exploration target of 4.1–11.2Moz AuEq behind the current 3.6Moz MRE, with a high-grade gold discovery announced in late August 2026 adding further resource growth potential alongside the metallurgical upgrade.
Bramaderos metallurgical results deliver material uplift to project economics
Sunstone Metals (ASX: STM) has released upgraded metallurgical recovery results from the Bramaderos Gold-Copper Project in southern Ecuador, announced on 1 September 2026. The revised average recoveries stand at 80% copper (up from 75% in the April 2026 Scoping Study) and 93% gold (up from 85% in the Scoping Study).
The company has confirmed these results are expected to have a material positive impact on all key project metrics, including potential gold and copper production, unit costs, and NPV. For a project already carrying a 3.6Moz AuEq resource, that is not a minor technical footnote.
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What the Bramaderos testwork found
Locked-cycle flotation confirms conventional processing pathway
Testwork was undertaken at Intertek Kamloops and overseen by Pitchblack Group, covering the two principal ore types at Bramaderos: Brama Diorite (DI) and Brama Breccia (IBX).
The best locked-cycle flotation results were strong across both ore types. For Diorite, the testwork achieved 83% copper recovery and 57% gold recovery to an 18% copper / 33g/t gold concentrate grade. For Breccia, results came in at 75% copper recovery and 54% gold recovery to a 17% copper / 48g/t gold concentrate.
Critically, optimisation testwork demonstrated that concentrate grades exceeding 24% copper are achievable, signalling further upside through ongoing process refinement. Low arsenic content was also confirmed, indicating production of 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.
The high-grade gold discovery at Bramaderos unveiled in late August 2026 adds further strategic context to the metallurgical results, as higher-grade material tends to respond particularly well to the flotation-plus-cyanidation flowsheet confirmed by this testwork.
Cyanidation of flotation tails maximises gold recovery
The headline gold recovery figures are driven by a two-stage process. Flotation plus regrind and cyanidation of flotation tails achieves approximately 94% gold recovery for Diorite and 92% for Breccia. These combined-process figures are what underpin the revised 93% average gold recovery assumption.
The confirmed processing flowsheet runs as follows: crushing, grinding, flotation, cyanidation of flotation tails, producing both a copper-gold concentrate and gold doré.
| Ore Type | Copper Recovery (Flotation) | Gold Recovery (Combined) | Concentrate Copper Grade | Concentrate Gold Grade |
|---|---|---|---|---|
| Brama Diorite (DI) | 83% | ~94% | 18% Cu | 33g/t Au |
| Brama Breccia (IBX) | 75% | ~92% | 17% Cu | 48g/t Au |
Understanding metallurgical recovery — why these numbers matter to investors
Metallurgical recovery is the percentage of a metal contained in ore that can actually be extracted and sold. Think of it as the efficiency rate of the processing plant. If a tonne of ore contains 1 gram of gold and the recovery rate is 85%, you sell the equivalent of 0.85 grams. The remaining 0.15 grams stays locked in the tailings.
Even a small improvement in recovery translates directly into more metal produced per tonne of ore mined. That means more revenue, lower unit costs per ounce, and a higher NPV, without needing to find more ore or spend more on drilling. The improvement here is not incremental. Copper recovery moved from 75% to 80% (a gain of 5 percentage points) and gold from 85% to 93% (a gain of 8 percentage points).
Now apply that across the Bramaderos resource: 220Mt at 0.50g/t AuEq for 3.6Moz AuEq (November 2025 Mineral Resource Estimate). Higher recoveries applied at that scale compound quickly into materially better project economics. Sunstone will now apply the updated recovery assumptions of 80% copper and 93% gold to all future AuEq calculations.
MD Patrick Duffy on what this means for Bramaderos
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.”
Duffy added that the outcomes are consistent with the company’s strategy to progressively grow the value of the overall Bramaderos Gold-Copper Project, supporting its continued advancement as a potential large-scale gold-copper development opportunity.
Significant new discoveries at Bramaderos reported in August 2026 sit alongside this metallurgical progress, collectively building the case for Bramaderos as a large-scale development candidate with both resource scale and processing confidence now better established.
What’s next for Sunstone and the Bramaderos project
The metallurgical results now feed directly into ongoing project studies. Next steps disclosed in the announcement include:
- Further variability testing currently underway
- Refining process optimisation parameters
- Validating metallurgical performance across additional ore domains
- Completing process circuit trade-off studies, including HPGR vs. SABC comparisons
- Incorporating metallurgical results into process plant design and operating cost estimation for ongoing project studies
Beyond Bramaderos, the company’s El Palmar project in northern Ecuador also has active news flow, with drilling expected to recommence in September 2026. Sunstone’s stated strategy is to progressively grow the value of Bramaderos toward a large-scale development outcome, with these metallurgical results providing what management describes as a robust foundation for that work.
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Sunstone Metals at a glance
Key facts for investor orientation:
- ASX Code: STM
- Projects: Two gold-copper projects in Ecuador — Bramaderos (southern) and El Palmar (northern)
- Bramaderos MRE: 220Mt at 0.50g/t AuEq for 3.6Moz AuEq (November 2025)
- Bramaderos Exploration Target: 4.1 – 11.2Moz AuEq (porphyry)
- El Palmar MRE: 64Mt at 0.60g/t AuEq for 1.2Moz AuEq
- JV Structure: Sunstone 87.5%, Jiangxi Copper 12.5% (loan carried)
- Team track record: Key personnel have been involved in significant porphyry and epithermal copper-gold discoveries at Cascabel (Ecuador) and Tujuh Bukit (Indonesia)
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