Sunstone Metals Drills New Gold-Copper Discovery at Porotillo, Bramaderos

Sunstone Metals Drills Up New Gold-Copper Discovery at Porotillo Outside Bramaderos Resource

Sunstone Metals Limited (ASX: STM) has reported a new gold-copper mineralisation discovery at the Porotillo prospect within its Bramaderos Gold-Copper Project in southern Ecuador. Drilling and trenching have defined a mineralised footprint across roughly 520m x 230m outside the existing 3.6Moz AuEq Mineral Resource. According to the ASX announcement, the new Porotillo results will be included in the December quarter 2026 Resource update, adding another potential growth area to the broader Bramaderos cluster.

The latest update matters because it extends mineralisation beyond the current resource boundary at a time when Sunstone is still receiving assay results from multiple prospects. Furthermore, the company confirmed that all 24 holes assayed from the recent programme at Porotillo, Copete and Melonal have returned long mineralised intersections, giving investors a large dataset of drilling success outside the existing resource.

Managing Director Patrick Duffy captured the significance of these results clearly. "We have outlined another very large body of mineralisation which we can include in the upcoming resource estimate. We are hitting very wide zones of gold and copper with every drill hole. We have a perfect strike rate so far in this programme, with all 24 holes returning extensive intersections of mineralisation. And every one of these holes is outside the 3.6Moz AuEq resource."

Latest Porotillo Drill Results Extend the Mineralised Footprint

In the ASX update, Sunstone reported assays from four more holes drilled at Porotillo: PTDD016, PTDD017, PTDD018 and PTDD019. All four intersected gold-copper mineralisation from surface, continuing the pattern seen in prior drilling at the prospect.

The strongest intersection from this batch came from PTDD017, which returned 196m at 0.62 g/t AuEq from surface, including 143m at 0.72 g/t AuEq. For investors, long intersections from surface can be important because they may support bulk-tonnage development potential if continuity and economics are confirmed through future work.

According to the company, PTDD017 also included 4.80m at 2.29 g/t AuEq, comprising 0.59 g/t gold and 1.00% copper, within what was described as a high-sulphidation epithermal structure. In practical terms, this refers to a shallower style of mineralisation formed by hot mineral-rich fluids, which can sometimes add local higher-grade zones above or within a larger porphyry system.

Sunstone confirmed that these latest holes extended mineralisation on the northeast, southeast and southwest margins of the Porotillo orebody. That is relevant because resource growth depends not only on grade, but also on continuity and the ability to define material over meaningful dimensions.

All 24 Holes Outside the Resource Have Hit Mineralisation

The broader drilling picture at Bramaderos remains one of the more important points in the announcement. Sunstone stated that all 24 holes assayed from the current drilling programme at Porotillo, Copete and Melonal returned mineralised intersections, and all of them sit outside the current Bramaderos resource.

A selection of intersections reported by the company shows consistent bulk widths across the programme:

This intercept profile is consistent with large porphyry-style systems, where grades are often moderate but spread across large rock volumes. According to Sunstone, grade shell interpretation at Porotillo and Copete indicates the stronger mineralisation is coherent and near-surface, associated with an oxide-sulphide transition zone that appears to have improved copper tenor in shallow areas.

That geological point may be important. Near-surface mineralisation can be more attractive in early economic studies because it may reduce strip ratios and support simpler mine planning, although no development outcome can be assumed from exploration results alone.

Trenching Adds Scale Ahead of the December Quarter Resource Update

How Does Surface Trenching Support the Resource Case?

The drilling programme has been supported by trenching and surface channel sampling across the prospects. At Porotillo, trench PO-6 was excavated as a southeast continuation of previously reported trench PO-5.

Sunstone confirmed that PO-6 returned 145.48m at 0.45 g/t AuEq. Combined with contiguous PO-5, which previously returned 462.22m at 0.55 g/t AuEq, the surface mineralised trend now totals 607.71m at 0.52 g/t AuEq and remains open to the northwest.

That is a sizeable surface expression for a prospect not yet included in the Mineral Resource Estimate. Trenching does not replace drilling, however it can help define continuity at surface and guide future drill targeting, particularly where rock exposure is limited.

In addition, Sunstone reported that drilling and trenching have now outlined significant mineralisation at Porotillo over a northwest-southeast extent of 530m and a northeast-southwest extent of up to 230m. Investors should refer to the company's ASX wording for the formal project description.

What Is a Porphyry Gold-Copper System?

Porphyry gold-copper systems are among the most common sources of large copper and gold deposits globally. They typically form around intrusive rocks, where mineral-rich fluids move through fractures and deposit metals over broad areas.

For investors, the main characteristics of a porphyry deposit are generally:

• Large tonnage potential, often across hundreds of millions of tonnes
• Broad mineralised intervals, rather than narrow veins
• Multiple payable metals, commonly gold, copper and silver
• Potential for open-pit mining, where mineralisation starts near surface

These systems are often described as low-to-moderate grade on a per-tonne basis. The investment appeal comes from scale. A deposit grading around 0.4 g/t to 0.6 g/t AuEq can still be significant if it extends over a very large rock volume.

Understanding AuEq and Key Terminology

Another key concept in the Sunstone announcement is AuEq, or gold equivalent. This converts the value of copper and silver into a gold-equivalent grade using assumptions about metal prices and recoveries. For Bramaderos porphyry mineralisation, Sunstone uses prices of US$1,800/oz gold, US$4.50/lb copper and US$22/oz silver, with estimated recoveries of 88% for gold, 85% for copper and 60% for silver.

A quick glossary of terms referenced throughout this update:

• AuEq: Gold equivalent, a combined measure converting multiple metals into a single gold-based grade
• JORC: The Australian reporting standard used for exploration results and mineral resources
• Indicated Resource: A resource category with higher confidence than inferred
• Inferred Resource: A lower-confidence resource category based on available geological data
• High-sulphidation epithermal: A shallower gold-copper mineralisation style that can occur above or around porphyry systems

Assays Pending and Deep Limon Drilling Provide the Next Catalysts

The current Porotillo update is not the end of the campaign. According to the announcement, Sunstone still has multiple assays pending before beginning the 2026 resource estimation process.

Pending results include:

• 4 additional drill holes at Melonal: MEDD004 to MEDD007
• 9 channel samples at Melonal: QM-5 to QM-13
• 1 drill hole at Copete: CPDD005
• 1 drill hole at Porotillo: PTDD020
• 4 trenches at Porotillo: PO-7 to PO-10

Sunstone confirmed these additional assay results are expected during August 2026, after which work on the resource update is set to commence. For investors, this creates a sequence of near-term newsflow rather than a single binary event.

Another important point highlighted in the report is the planned start of a 1,200m deep exploration hole at the Limon porphyry target in early August. Management said the hole is designed to test the porphyry gold-copper system below and southwest of the shallow Limon gold-silver deposit.

A deep porphyry hole is a different style of catalyst from resource extension drilling. While higher risk, it may test a larger conceptual target that could add a new mineralised centre within the broader Bramaderos project if mineralisation is confirmed.

Bramaderos Resource Base and the Wider Investment Context

Sunstone's existing November 2025 Mineral Resource Estimate for Bramaderos stands at 220Mt at 0.50 g/t AuEq for 3.6Moz AuEq, before adding any of the newer Porotillo, Copete or Melonal mineralisation.

The announcement also reiterated broader exploration upside already disclosed by the company. Bramaderos carries a porphyry Exploration Target of 4.1Moz to 11.2Moz AuEq within 315Mt to 505Mt, plus a Limon epithermal Exploration Target of 0.9Moz to 1.7Moz AuEq within 30Mt to 44Mt. These figures are conceptual in nature and are not Mineral Resources.

Outside Bramaderos, Sunstone also holds the El Palmar Project in northern Ecuador, which carries an existing resource of 64Mt at 0.60 g/t AuEq for 1.2Moz AuEq. El Palmar also holds a large exploration target, although that sits outside the scope of the current Bramaderos drilling update.

Ownership is another practical consideration. Sunstone holds an 87.5% interest in the Bramaderos joint venture, while Jiangxi Copper holds a 12.5% loan-carried interest. That means most of the direct exposure to any Bramaderos resource growth remains with Sunstone.

Why the Sunstone Update Matters to ASX Investors

The latest Bramaderos update adds meaningful weight to the company's resource growth case. First, the 24-from-24 drilling record outside the existing resource indicates strong mineralisation continuity across multiple targets. Second, Porotillo has now been defined over dimensions large enough to be relevant to the upcoming resource update.

The combination of near-surface intersections, broad trench results, and pending assays means the December quarter 2026 update is shaping up as a material milestone. Investors will likely focus on how much of the new Porotillo, Copete and Melonal mineralisation converts into formal resource tonnes and ounces.

The second layer of interest comes from Limon. If the upcoming 1,200m deep hole identifies a larger porphyry system beneath the shallow gold-silver deposit, it could add another exploration front within a project that already hosts multiple mineralised centres.

For now, the ASX announcement points to a company still in expansion mode at Bramaderos. With new mineralisation being defined outside the current 3.6Moz AuEq resource and more assays due in August, Sunstone's next steps will be closely tied to whether this exploration success translates into a larger December quarter resource base.

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