Sunstone Metals Ltd (ASX:STM) has boosted the mineral resource estimate (MRE) at its Bramaderos gold-copper project in southern Ecuador by 33% to 3.6 million ounces of gold equivalent (AuEq), paving the way for scoping studies on a potential open-pit development.
The updated November 2025 MRE now sits at 220 million tonnes at 0.50 g/t AuEq (0.33 g/t gold, 0.10% copper and 1.16 g/t silver) at a 0.30 g/t AuEq cut-off grade, equivalent to 3.6 million ounces of gold-equivalent metal.
Notably, the higher-confidence Indicated component has tripled to 600,000 ounces AuEq, up from 200,000 ounces in the 2022 estimate, providing a stronger foundation for economic studies. The balance of 2.9 million ounces AuEq is in the Inferred category.
Managing director Patrick Duffy said the result confirmed Bramaderos as a large-scale gold-copper system with room to grow.
“This is an outstanding result which adds huge additional value to Bramaderos and shows beyond doubt that it is rapidly emerging as a world-class project in an ideal location,” Duffy said. “The project now boasts a resource of 3.6Moz of gold-equivalent, with grades that outperform those of many other major open-pit porphyry projects and has a clear path to rapid, substantial increases.”
Resource underpins open-pit development case
The updated MRE is constrained within preliminary open-pit shells over the Brama-Alba-Melonal porphyry deposits, all of which come to surface and are expected to be amenable to conventional, low-strip open-pit mining.
Overview of key prospects on the Bramaderos project, the Brama-Alba-Melonal resource area, and Exploration Target areas defined on the Bramaderos properties.
The company said the 900,000-ounce AuEq increase since December 2022 was driven primarily by:
- additional Inferred material from drilling at Melonal (about 355,000 ounces AuEq), and
- a larger contribution from Brama-Alba (about 533,000 ounces AuEq) following an updated geological model and new drilling data near Melonal.
Pricing assumptions used for the update were broadly consistent with the prior estimate, with gold held at US$1,800 per ounce and copper increased slightly from US$4.20 to US$4.50 per pound, contributing only a minor uplift to contained metal.
Earlier metallurgical test work on Brama-Alba-Melonal mineralisation reported gold recoveries of about 88% and copper recoveries above 85% using a combined flotation and leach flowsheet, with concentrate grades exceeding 20% copper, supporting the potential for a conventional processing route.
“The resource is all comfortably within open-pit depths, and with 600,000oz AuEq now in the higher-confidence Indicated category, we will undertake a scoping study that will underscore the project’s immense value,” Duffy said. The scoping study is expected to examine a large-scale open-pit operation over the Brama-Alba-Melonal cluster.
Brama-Alba-Melonal drill status plan showing the status of Sunstone drilling, historical drilling, plus trenching and surface channel sampling for the November 2025 MRE on a backdrop of gold-in-soil results.
Exploration target grows to 5–13Moz AuEq
Alongside the MRE, Sunstone has updated and expanded its Exploration Target for Bramaderos, incorporating both porphyry and epithermal systems.
The company now estimates:
- A porphyry Exploration Target of 315–505 million tonnes at 0.41–0.69 g/t AuEq for 4–11 million ounces AuEq, covering Brama-Alba extensions, Melonal, the upper part of Limon and the new Copete-Porotillo area.
- A separate Limon higher-grade epithermal Exploration Target of 30–40 million tonnes at 0.9–1.2 g/t AuEq for 0.9–1.7 million ounces AuEq.
Combined, the updated Bramaderos project Exploration Target stands at 345–549 million tonnes at 0.45–0.73 g/t AuEq for 5.0–12.9 million ounces AuEq.
A significant contributor to the expansion is the new Copete-Porotillo porphyry Exploration Target of 135–180 million tonnes at 0.4–0.6 g/t AuEq (0.25–0.40 g/t gold and 0.10–0.12% copper), equating to 1.7–3.5 million ounces AuEq. This target reflects extensive surface sampling, trenching and historic drilling, which have outlined a coherent mineralised corridor spanning roughly 700 metres in length.
Drilling and scoping study plans for 2026
With the updated MRE in hand, Sunstone plans to commence a scoping study on a base-case development scenario for Brama-Alba during the first half of 2026, focused on an initial open-pit operation.
Long-section (100m section thickness) through Brama-Alba and showing the November 2025 block model, diamond drillholes with AuEq assays and the modelled pit. Areas are also show where the resource remains open below the pit and form part of the Brama-Alba porphyry exploration target.
In parallel, the company is prioritising drilling aimed at growing the resource and converting portions of the Exploration Target into future resource updates. Key programs planned for 2026 include:
- step-out and infill drilling across the Brama-Alba-Melonal porphyry system,
- further drilling at the Limon epithermal system, where previous holes have delivered broad high-grade gold-equivalent intercepts, and
- initial and follow-up drilling across the Copete-Porotillo corridor to test the newly defined porphyry target at depth.
Sunstone sees Bramaderos, together with its El Palmar copper-gold project in northern Ecuador, as the foundation for a potential multi-decade gold-copper production centre in a jurisdiction with established infrastructure and growing interest from major miners.
Location of Sunstone’s Bramaderos, El Palmar, and Verde Chico projects in Ecuador.