Sunstone reveals a larger Bramaderos mine-building platform

Bramaderos Resource Reaches 6.2Moz AuEq

Sunstone Metals Limited (ASX:STM) has added 2.6 million ounces of gold equivalent to its Bramaderos project in southern Ecuador, lifting the JORC Mineral Resource Estimate by 72% to 464 million tonnes at 0.42g/t AuEq, or 6.2Moz. The estimate is reported above a 0.30g/t AuEq cut-off within an optimised pit shell, intended to demonstrate reasonable prospects for eventual open-pit extraction.

The more consequential shift is in confidence rather than headline ounces. Indicated Resources now stand at 229Mt at 0.45g/t AuEq for 3.3Moz, compared with 40Mt and 0.6Moz in the November 2025 estimate. No Measured Resources or Ore Reserves have been reported.

Drilling Converts Copete and Porotillo

Growth came from three sources: additional drilling and trenching at Melonal contributed 0.3Moz AuEq; the maiden Copete-Porotillo Resource added 1.3Moz; and a larger pit shell reflected higher commodity-price assumptions and improved gold recovery inputs. The latest resource is based on 91 drill holes totalling 36,855 metres, alongside 8,628 metres of trenching and channel sampling.

The new estimate follows a 30-hole resource-growth program in which all holes reportedly intersected significant mineralisation. Melonal now contributes 1.4Moz AuEq, while Copete-Porotillo contributes 1.3Moz; the established Brama-Alba-Melonal cluster remains the larger component at 4.9Moz.

Exploration Target Keeps Expansion Case Alive

Sunstone has also retained a conceptual Exploration Target additional to the MRE of between 4.4Moz and 11.2Moz AuEq across 300Mt to 474Mt. That range combines a 3.5Moz to 9.5Moz porphyry target with the separate Limon epithermal target of 0.9Moz to 1.7Moz. The target is not a Mineral Resource: the company states that there has been insufficient exploration to establish one, and further drilling may not produce a resource estimate.

The porphyry target was revised after material was converted into the MRE. That conversion is an encouraging feature of the exploration story, but it also makes the upper ounce range particularly conceptual. Areas including Sandia, Playas and Yeso were excluded because drilling is not yet sufficient to support an Exploration Target.

Metallurgy and Mine Studies Remain the Test

For Brama-Alba and Melonal, metallurgical work indicates a combined flotation and leach circuit could recover more than 80% of copper and about 93% of gold, producing a concentrate above 18% copper. The updated MRE uses overall assumptions of 91% gold recovery, 78% copper recovery and 60% silver recovery, with metal equivalents calculated using US$3,000 gold, US$6 copper and US$40 silver prices.

Porotillo is less settled. Its deeper transitional profile contains more oxide copper, and first-phase test work is continuing. The current estimate therefore applies lower recovery assumptions to transitional material: 76% for gold and 65% for copper. Against that backdrop, Sunstone is evaluating a new Scoping Study, while planned drilling will target resource conversion, extensions between Melonal and Copete, ground south of Porotillo and higher-grade potential between Melonal and Alba.

The result materially improves the geological inventory available for mine planning, but it is not yet a development decision. The resource has not been independently audited by a third party, Porotillo metallurgy remains incomplete and Sunstone’s own filing says future exploration and study work will depend on the company’s funding capacity. The next useful evidence will be whether drilling converts more of the Inferred 2.9Moz, and whether the proposed study can turn a large pit-constrained inventory into a credible operating case.