Sunstone Metals Limited (ASX: STM) released on 21 April 2026 the Open Pit Scoping Study for its 87.5%-owned Bramaderos Gold-Copper Project in Ecuador. The Study confirms the project's potential as a high-margin, multi-decade gold-copper operation based on the November 2025 Mineral Resource Estimate of 3.6Moz AuEq. At a Base Case gold price of US$3,500/oz, the project delivers NPV7.5% of US$1.4 billion pre-tax and US$0.9 billion post-tax, IRRs of 39% pre-tax and 28% post-tax, and a 34-month capital payback. The Spot Case (US$5,000/oz gold) generates NPV7.5% of US$2.9 billion pre-tax and US$1.9 billion post-tax at 70%/50% IRRs, with payback shortened to 19 months.

The open pit envisages a single operation processing 220Mt at 0.44 g/t AuEq for 3.1Moz AuEq of contained gold, producing an average of 135kozpa AuEq in the first 8 years and 120kozpa AuEq over an initial 23-year mine life, at AISC of US$1,499/oz (after by-product credits). Pre-production capital cost is estimated at US$511 million. Sunstone has now committed to progress the project directly to a Pre-Feasibility Study (PFS), running in parallel with continued resource-growth exploration targeting an additional 5.0–12.9Moz AuEq.

Key Facts at a Glance

  • Company: Sunstone Metals Limited
  • ASX Code: STM
  • Announcement Date: 21 April 2026
  • Project: Bramaderos Gold-Copper Project, Ecuador (87.5% STM ownership)
  • Resource Base: 3.6Moz AuEq (November 2025 MRE)
  • Pit Schedule: 220Mt @ 0.44 g/t AuEq for 3.1Moz AuEq contained gold
  • Life-of-Mine Production: 2.7Moz AuEq (Indicated + Inferred)
  • Mine Life: 23 years (initial)
  • Production Profile: 135kozpa AuEq years 1-8; 120kozpa AuEq LOM average
  • Throughput: 10Mtpa single-line mill
  • AISC: US$1,499/oz (after by-product credits)
  • Pre-production Capex: US$511 million
  • Base Case (US$3,500/oz): NPV7.5% US$1.4B pre-tax / US$0.9B post-tax; IRR 39% pre-tax / 28% post-tax; 34-month payback
  • Spot Case (US$5,000/oz): NPV7.5% US$2.9B pre-tax / US$1.9B post-tax; IRR 70% pre-tax / 50% post-tax; 19-month payback
  • Funding Requirement: ~US$525M
  • Metallurgy: SAB-float-leach — avg 85% Au recovery, 75% Cu recovery
  • Exploration Target: additional 5.0–12.9Moz AuEq (345Mt–549Mt @ 0.45–0.73 g/t AuEq)

Announcement Overview

The Scoping Study has been completed to an accuracy of -30% to +45% in line with industry standards. Roughly 20% of the Life of Mine Production Target is in the Indicated Mineral Resource category and 80% is in the Inferred Mineral Resource category — although Sunstone has disclosed that Base Case post-tax payback is achieved four months after the initial Indicated-only production period, and that a processing schedule using only Indicated material delivers post-tax payback of 26 months. The Study therefore meets JORC guidance for including Inferred Resources in the production target.

The Study assumes commodity prices of US$3,500/oz gold, US$5.00/lb copper and US$50/oz silver in the Base Case, and US$5,000/oz gold (Spot Case). All outcomes are presented on a 100% basis; Sunstone's attributable interest is 87.5%.

Company Background: Sunstone Metals Limited

Sunstone Metals Limited (ASX: STM) is a gold-copper developer focused on its 87.5%-owned Bramaderos Project in southern Ecuador. The Project benefits from access to highway and port infrastructure, secured water and power, minimal pre-strip requirements, and a supportive local community. Sunstone's registered office is at Level 31, 120 Collins Street, Melbourne.

Detailed Analysis

Project Economics — Base and Spot Cases

The differential between Base (US$3,500/oz) and Spot (US$5,000/oz) scenarios is meaningful: NPV7.5% more than doubles (US$1.4B → US$2.9B pre-tax), IRRs step up sharply (39% → 70% pre-tax), and payback shortens from 34 months to 19 months. Notably, the Spot Case is approximately US$1,300/oz below actual spot gold prices referenced by Sunstone, meaning the Spot Case itself may still be conservative.

Operating and Capital Profile

Pre-production capex of US$511M is modest relative to projects of similar scale in other jurisdictions, reflecting existing infrastructure access (highway, port, water, power) and minimal pre-strip requirements. AISC of US$1,499/oz after by-product credits positions Bramaderos comfortably in the industry cost curve at current gold prices.

Metallurgy and Processing

The SAB-float-leach process plant supports average recoveries of 85% gold and 75% copper, with silver also recovered at approximately 60%. A single-line 10Mtpa throughput makes the operation scalable and simpler from an operational standpoint.

Growth and Optionality

The exploration target of an additional 5.0-12.9Moz AuEq is conceptual but substantial. If successful, the Company envisages a Stage 2 expansion increasing total throughput to 20-30Mtpa — funded from future operating cash flows rather than additional equity.

Funding Pathway

Approximately US$525M of funding is likely required. Sunstone has disclosed that this may take the form of debt and/or equity, and that alternative "value realisation" strategies such as sale, partial sale or joint venture are also possible outcomes.

Strategic Significance

Bramaderos transitions from a "major resource but uncertain economics" story to a "study-backed, multi-decade project with strong economics at conservative prices" story. The step to PFS, combined with continued exploration to expand the resource, sets up a multi-year derisking trajectory.

Market and Investor Impact

The Scoping Study establishes a defensible valuation framework for STM. At Base Case US$0.9B post-tax NPV on 87.5% ownership, Sunstone's attributable Project NPV is meaningful relative to typical explorer/developer market caps in its peer set. Catalyst pathway from here includes: PFS scope and timing, exploration updates on the 5.0–12.9Moz AuEq target, funding discussions, and Ecuadorian permitting milestones.

What This Means for Investors

Investors now have a quantified pathway to compare Bramaderos against peer projects. The Base Case is explicitly stated at a gold price US$1,300/oz below spot, which investors can interpret as significant built-in conservatism. Execution risk remains the principal variable — PFS, funding, permitting and construction all lie ahead.

Risks and Opportunities

Risks

  • Study accuracy: Scoping Study has -30% to +45% precision; PFS/DFS could change outcomes.
  • Resource category: ~80% of Production Target is in Inferred category, lower geological confidence.
  • Funding risk: ~US$525M debt/equity required; dilutive capital raising possible.
  • Jurisdictional risk: Ecuador fiscal, environmental and community approvals.
  • Commodity price risk: Base Case US$3,500/oz vs spot is supportive, but economics are cycle-sensitive.

Opportunities

  • Strong Base Case economics: 39% pre-tax IRR, 34-month payback, US$1.4B NPV.
  • Large exploration target (5.0-12.9Moz AuEq) supports resource growth.
  • Stage 2 expansion to 20-30Mtpa funded from operating cash flows.
  • Existing infrastructure reduces capex burden.
  • Potential alternative value realisation via sale/JV.

Key Takeaways

  • Base Case: NPV7.5% US$1.4B pre-tax / US$0.9B post-tax; IRR 39%/28%.
  • 23-year initial mine life; 2.7Moz AuEq production.
  • AISC US$1,499/oz after by-product credits.
  • Pre-production capex US$511M; total funding ~US$525M.
  • STM moving immediately to Pre-Feasibility Study plus continued exploration.

Bottom Line

Bramaderos now has a Scoping Study consistent with being a tier-one gold-copper asset in the making: strong economics at conservative prices, clear resource growth potential, and a defined derisking pathway through PFS. Execution, funding and permitting will decide the timeline to production.

Disclaimer

This article is based solely on the corresponding ASX announcement and is for informational purposes only. It does not constitute financial, investment, legal, or tax advice. Investors should conduct their own due diligence and consult a licensed financial adviser before making investment decisions. Past performance is not indicative of future results.