Capstone Copper Completes Acquisition of San Pietro Copper Concessions, Consolidating the Mantoverde-Santo Domingo Copper District

Company Website: https://www.capstonecopper.com VANCOUVER, British Columbia -- (Business Wire) Capstone Copper Corp. (“Capstone” or the “Company”) (TSX:CS) (ASX:CSC) is pleased to announce that it has completed the acquisition of the copper assets at the San Pietro copper-gold-iron-cobalt project (“San Pietro” or the “Project”), strategically located between Capstone’s Mantoverde, Santo Domingo, and Sierra Norte properties in Chile’s Atacama Region (the “Transaction”). Unless otherwise stated, results are presented in United States dollars on a 100% basis. This press release features multimedia. View the full release here: https://www.businesswire.com/news/home/20260831848151/en/ Figure 1: Within a ~20km radius in the Mantoverde-Santo Domingo District, Capstone’s mineral concessions contain ~1.6 billion tonnes(2) of Measured & Indicated Mineral Resources inclusive of Mineral Reserves, in addition to ~1.4 billion tonnes(2) of Inferred Mineral Resources, surrounded by key infrastructure and located at low elevation San Pietro adds approximately 16,000 hectares of highly prospective, underexplored ground to Capstone’s district-scale land position. The Project includes the Rincones and Colla deposits, which host an existing NI 43-101 compliant Inferred Mineral Resource of 492 million tonnes grading 0.23% copper and 0.05 g/t gold, including a higher-grade component (see Figure 3). The acquisition provides an immediate increase in mineral inventory and a platform for further resource growth. Under the terms of the Transaction, Capstone paid total consideration of $25 million in Capstone shares(1) to New Golden Exploration Chile SpA (“NGE”), a joint venture indirectly owned by Golden Arrow Resources Corp. (“Golden Arrow”) (75.019%) and its joint venture partner, Sociedad de Servicios Andinos SPA (“SSA”) (24.981%). The acquisition represents a cost-effective expansion of Capstone’s position in the Atacama. Transaction Highlights Consolidates a world-class copper district in Chile’s Atacama region Adds ~16,000 hectares of highly prospective, underexplored copper concessions to Capstone’s existing land position (see Figure 1) Strengthens the continuity of Capstone’s district-scale footprint, as San Pietro is strategically positioned within the Mantoverde-Santo Domingo District (“MV-SD District”) (see Figure 2) Builds on the acquisition of Sierra Norte in 2024 and the exploration option agreement signed with Empresa Nacional de Minería (“ENAMI”) in 2025 Creates a platform for integrated district development Combines ~60,000 hectares under Capstone’s ownership with a further ~18,000 hectares including the ENAMI option agreement Enables Capstone to leverage its in-depth regional experience to advance optimization opportunities, identify potential synergies and progress a coordinated district development strategy Creates opportunity to leverage existing and planned district infrastructure to enable multiple pathways for future optionality to be executed Adds significant mineral inventory and optionality around district feed sources The Rincones and Colla deposits host a large Inferred Mineral Resource of 492 million tonnes at 0.23% copper and 0.05g/t gold (see Figure 3) Based on a recommended exploration program, Capstone anticipates defining a higher-grade portion within the existing Resource footprint This resource adds immediate mineral inventory, supports potential future resource growth and may provide incremental oxide and sulphide feed for district processing Unlocks substantial exploration upside near existing, and future, district infrastructure Beyond the defined Mineral Resource, Capstone has identified several highly prospective copper exploration targets at San Pietro along regional structures associated with mineralization at Mantoverde, Santo Domingo and Sierra Norte Cashel Meagher, Capstone’s President and Chief Executive Officer, commented: “Capstone’s acquisition of San Pietro marks another step in the consolidation of the Mantoverde-Santo Domingo District. Located adjacent to Santo Domingo, and between Mantoverde and Sierra Norte, the Project is a natural fit within a region where we have existing and permitted infrastructure, deep knowledge of the local geology, and an experienced operating and project development team. Following our acquisition of Sierra Norte in 2024 and the exploration option agreement signed with ENAMI in 2025, this Transaction further expands our footprint in the top-tier region of the Atacama. We look forward to integrating San Pietro into our district exploration and development plans as we pursue opportunities to unlock transformational copper production growth.” Figure 3: Rincones and Colla Inferred Mineral Resource Estimate Inferred Mineral Resource Estimate for Rincones & Colla Deposits at San Pietro Property Reported within US$4.80/lb Cu Pitshell at 0.30% CuEq Cut-off Category Tonnes (Mt) Average Grade Contained Metal Cu (%) Au (g/t) Co (ppm) Fe (%) Cu (Mlb) Au (Koz) Co (Mlb) Fe (Blb) Inferred – Oxide 83 0.23 0.06 96 14.80 759 150 17 27 Inferred – Sulphide 410 0.23 0.05 99 14.35 3,686 620 90 130 Total 492 0.23 0.05 99 14.43 4,444 770 107 157 The Rincones and Colla initial resource estimate comprises 83 million tonnes of oxide Inferred Mineral Resource and 410 million tonnes of sulphide Inferred Mineral Resource. The Mineral Resource was derived from the NI 43-101 technical report titled “Mineral Resource Estimate for the San Pietro Copper-Gold-Iron-Cobalt Project” completed by independent qualified persons (Dr. Bruce David, PhD, FAusIMM and Susan Lomas, P.Geo) with an effective date of January 24, 2025 prepared for Golden Arrow Resources Corporation. The report can be found on SEDAR+. To the best of Capstone’s knowledge, information and belief, there is no new material scientific or technical information that would make the disclosure of the Mineral Resource inaccurate or misleading. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. Mineral Resources are reported within US$4.80/lb pitshell using a cut-off grade of 0.3%. The San Pietro deposit will require further evaluation including drilling to verify the mineral resource estimate. Figure 4: Estimated Mineral Reserves & Resources for Mantoverde and Santo Domingo Estimated Mineral Resources MINERAL RESOURCES – Inclusive of Mineral Reserves CONTAINED METAL   Category kt TCu SCu Zn Pb Mo Ag Au Fe Co S Cu Zn Pb Mo Ag Au Fe Co % % % % % g/t g/t % ppm % kt kt kt kt koz koz mt kt Santo Domingo Measured 134,000 0.51 - - - - - 0.07 26.9 - - 679 - - - - 293 36 - Indicated 413,000 0.25 - - - - - 0.03 n/a - - 1,025 - - - - 449 95 - 31-Mar-2024 M&I 547,000 0.31 - - - - - 0.04 n/a - - 1,704 - - - - 742 131 -   Inferred 230,000 0.21 - - - - - 0.03 n/a - - 477 - - - - 200 46 -         Mantoverde Measured 174,942 0.56 - - - - - 0.10 - 178 - 988 - - - - 588 - 31 Sulphides Indicated 320,165 0.41 - - - - - 0.10 - 115 - 1,308 - - - - 1,035 - 37 (Flotation) M&I 495,107 0.46 - - - - - 0.10 - 137 - 2,296 - - - - 1,623 - 68   Inferred 550,089 0.37 - - - - - 0.08 - 33 - 2,035 - - - - 1,416 - 18         Sulphides Mixed Measured 33,048 0.44 - - - - - 0.09 - 76 - 145 - - - - 92 - 3 (Flotation) Indicated 35,335 0.35 - - - - - 0.08 - 90 - 124 - - - - 96 - 3   M&I 68,383 0.39 - - - - - 0.08 - 83 - 269 - - - - 188 - 6   Inferred 19,801 0.29 - - - - - 0.07 - 14 - 57 - - - - 42 - 1         Oxides + Mixed Measured 87,076 0.43 0.33 - - - - - - - - 283 - - - - - - - (Heap Leach) Indicated 53,909 0.39 0.30 - - - - - - - - 161 - - - - - - -   M&I 140,985 0.41 0.32 - - - - - - - - 444 - - - - - - -   Inferred 8,111 0.38 0.28 - - - - - - - - 23 - - - - - - -         Oxides + Mixed Measured 144,629 0.22 0.15 - - - - - - - - 210 - - - - - - - (Dump Leach) Indicated 140,518 0.21 0.14 - - - - - - - - 199 - - - - - - -   M&I 285,147 0.22 0.15 - - - - - - - - 409 - - - - - - - 31-Dec-2025 Inferred 59,985 0.22 0.13 - - - - - - - - 80 - - - - - - - Mineral Resources take into account mining activities to the effective date, where applicable and are reported insitu, using the 2014 CIM Definition Standards. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. Mineral Resources are reported inclusive of the Mineral Reserves. All Mineral Resources are exclusive to dilution and mining recovery factors. All contained metals are reported at 100% except as stated. Rounding as required by reporting guidelines may result in apparent summation differences between tonnes, grade and contained metal content. Grade TCu% refers to total copper grade in percent sent to the mill for metallurgical recovery by flotation. Grade SCu% refers to soluble copper grade in percent sent to the leaching processes. Grade ICu% refers to insoluble copper grade in percent, based on TCu% minus SCu%. Contained ounces (oz) are troy ounces. COG is cut-off grade. NSR is net smelter return. M&I = Measured & Indicated. All amounts in US$ unless otherwise specified. Stockpiled material is treated as Mineral Resources, described below. See Technical Reports filed under Capstone Copper’s profile on SEDAR+ for further information. Peter Amelunxen, P. Eng., Senior Vice President, Technical Services at Capstone Copper is the Qualified Person responsible for the Mineral Resource estimates for the Santo Domingo, Iris, Iris Norte and Estrellita deposits, effective March 31, 2024. Mineral Resources for the Santo Domingo, Iris and Iris Norte deposits are reported using a net smelter return (NSR) cut-off value of US$9.85/t. NSR is calculated using average long-term prices of US$4.10/lb Cu, US$1,600/oz Au, and Fe prices that depend on the expected grade of the Fe concentrate (US$94.75/dmt or $129.77/dmt or $140.26/dmt Fe concentrate). Mineral Resources are constrained by preliminary pit shells derived using a Lerchs–Grossmann algorithm and the following assumptions: pit slopes 36.3°- 47.9°; mining cost is calculated using a function that depends on where the material comes from (Santo Domingo or Iris Norte) and its destination (dumps, plant or stock); processing cost based on Fe concentrate routing code (including G&A costs); processing recovery based in the recovery equations for copper, gold, and iron as detailed above. For the Estrellita deposit, Mineral Resources are reported using an NSR cut-off value of US$9.63/t. NSR is calculated using average long-term prices of US$4.10/lb Cu and US$1,600/oz Au; only copper, and gold were considered in the NSR calculation (iron was excluded). Estrellita Mineral Resources are constrained by preliminary pit shells generated using a Lerchs–Grossmann algorithm and the following assumptions: pit slopes 43º; mining cost of US$1.55/t, processing cost of US$9.46/t (including G&A cost); processing recovery are calculated based in the recovery curves for copper and gold. The average Iron grades for the Project (Total Indicated, Total Measured plus Indicated, and Total Inferred Resources) cannot be calculated because Estrellita does not contain iron resources. Peter Amelunxen, P. Eng., Senior Vice President, Technical Services at Capstone Copper is the Qualified Person responsible for the Mineral Resource estimates at the Mantoverde Mine effective December 31, 2025. Mineral Resources are reported on a 100% basis. The attributable percentage to Capstone Copper is 69.993%. COG varies per zone and recovery process: Flotation: Sulphide: TCu ≥ 0.20% and oxidation state=3, Mixed: TCu ≥ 0.20% and SCu/TCu ≤ 50% and oxidation state=2. Dump Leach: Oxide: 0.10% ≤ SCu < 0.20% and oxidation state=1, Mixed 0.10% ≤ SCu < 0.20% and SCu/TCu > 50% and oxidation state=2. Heap Leach: Oxide: SCu ≥ 0.20% and oxidation state=1, Mixed: SCu ≥ 0.20% and SCu/TCu > 50% and oxidation state=2. Flotation recovery is based on a geometallurgical model, 90.44%TCu and 67.87% Au average for Sulphides and 72.77% TCu and 61.73% Au average for Mixed. Heap Leach recovery is based on operating data, expressed in algorithms per mineral model zone considering both SCu and CaCO₃ grades. The average heap leach recovery is 67.64% SCu, with an additional 50% metal recovered achieved through the bioleaching process. For dump leaching, the recovery averages 38.9% SCu, based on operational data. Dump recovery is 37.74%SCu (based on operating data). The Mineral Resource pit is based on $4.00/lb Cu and $1,700/oz Au based on long-term forecast pricing. Estimated Mineral Reserves MINERAL RESERVES CONTAINED METAL   Category kt TCu SCu ICu Zn Pb Mo Ag Au Fe Cu Zn Pb Mo Ag Au Fe % % % % % % g/t g/t % kt kt kt kt koz koz Mt Santo Domingo Proven 130,945 0.52 - - - - - - 0.07 27.2 675 - - - - 291 13 Probable 305,111 0.25 - - - - - - 0.04 26.2 761 - - - - 346 56 31-Mar-2024 Total 436,056 0.33 - - - - - - 0.05 26.5 1,435 - - - - 637 68       Mantoverde Proven 209,871 0.55 - - - - - - 0.10 - 1,146 - - - - 675 - Sulphides + Mixed Probable 174,347 0.39 - - - - - - 0.09 - 686 - - - - 504 - (Flotation) Total 384,219 0.48 - - - - - - 0.10 - 1,833 - - - - 1,179 -       Oxides Proven 125,411 - 0.21 - - - - - - - 259 - - - - - - (Dump+Heap Leach) Probable 70,356 - 0.19 - - - - - - - 131 - - - - - - 31-Dec-2025 Total 195,768 - 0.20 - - - - - - - 390 - - - - - - Mineral Reserves take into account mining activities as stated, where applicable. Rounding as required by reporting guidelines may result in apparent summation differences between tonnes, grade and contained metal content. Grade TCu% refers to total copper grade in percent sent to the mill for metallurgical recovery by flotation. Grade SCu% refers to soluble copper grade in percent sent to the leaching processes. Grade ICu% refers to insoluble copper grade in percent, based on TCu% minus SCu%. All Mineral Reserve estimates take into account dilution and mining recovery factors. Contained ounces (oz) are troy ounces. COG is cut-off grade. NSR is net smelter return. All amounts in US$ unless otherwise specified. Stockpiled material is included in the Mineral Reserves, described below. See Technical Reports filed under Capstone Copper’s profile on SEDAR+ for further information. Peter Amelunxen, P.Eng., Senior Vice President, Technical Services at Capstone Copper is the Qualified Person responsible for the Santo Domingo Project Mineral Reserve effective March 31, 2024. Mineral Reserves are reported as constrained within Measured and Indicated Resources and pit designs optimized using the following economic and technical parameters: metal prices of US$3.75/lb Cu, US$1,400/oz Au and Fe prices ranging from US$69/dmt to US$114.51/dmt based on the Fe grade in concentrate (net of Fe concentrate transport costs); average recovery to concentrate is 90.1% for Cu and 56.3% for Au, with magnetite concentrate recovery varying on a block-by-block basis; copper concentrate treatment charges of US$80/dmt, U$0.08/lb of copper refining charges, US$5.0/oz of gold refining charges, US$40/wmt and US$25.75/dmt for shipping copper and iron concentrates respectively; waste and ore mining cost of $1.55/t and process and G&A+SUSEX of US$9.77/t processed; average pit slope angles that range from 36.3° to 47.9°; a 2% royalty rate assumption and an assumption of 100% mining recovery. No formal production has occurred from the Santo Domingo property area. Peter Amelunxen, P. Eng., Senior Vice President, Technical Services at Capstone Copper is the Qualified Person responsible for the Mineral Reserve at the Mantoverde Mine effective December 31, 2025. Mineral Reserves are reported on a 100% basis as constrained within Measured and Indicated Resources and pit designs included within the mine schedule. The attributable percentage to Capstone Copper is 69.993%. The block model is considered to be fully diluted and no dilution or mining losses are applied. The pit designs and mine plan were optimized using assumed metal prices of $3.50/lb Cu and $1,500/oz Au. Mineral Reserves for flotation are estimated above a 0.20% Total Copper (TCu) cut-off. Mineral Reserves for leach are estimated above a 0.10% Soluble Copper (SCu) cut-off for Dump leach, with a variable Heap cut-off between 0.16% and 0.21% SCu to reflect ore availability. Leach-grade material mined after 2037 was scheduled as waste. LOM feed to flotation averaged 87.7% total copper recovery and 65.3% gold recovery. Average heap leach recovery applied in Mine Planning was 71.5% of SCu and 50% of ICu, where ICu = TCu – SCu. Average dump leach recovery applied was 38.0% of SCu. Mineral Reserves considered the following average costs: mining cost of $1.87 per tonne moved; $10.11/t flotation processing+tails+G&A; $0.31/lb TC/RC+freight for flotation; $10.14/t heap+G&A; $1.78/t dump leach; $0.35/lb SX/EW costs; and $0.05/lb cathode selling cost. Heap leach Reserve figures include the costs and benefits of bioleaching; the contained metal reported in the table considers SCu only. This excludes insoluble copper, of which a portion is expected to be recovered from bioleaching in the heap leach process. Inter-ramp angles in rock vary from 52° to 59°. The LOM strip ratio is 2.7:1. Figure 5: Historical Mineral Resource Estimate for Sierra Norte Category Mt TCu SCu Cu % % kt Carmen-Paulina Measured 7.5 0.47% 0.16% 35.5 Indicated 63.5 0.46% 0.10% 292.0 Inferred 25.1 0.40% 0.04% 101.5 Total 96.1 0.45% 0.09% 429.0 Esther Measured 0.7 0.42% 0.26% 3.0 Indicated 3.3 0.40% 0.24% 13.3 Inferred 0.1 0.35% 0.22% 0.3 Total 4.1 0.40% 0.24% 16.6 The Historical Mineral Resource was derived from the report “Actualización del Modelo Geológico y de la Estimación de Recursos Minerales del Proyecto Diego de Almagro” completed by Amec Foster Wheeler with an effective date on April 29, 2016 prepared for Alxar S.A. The historical estimates are strictly historical in nature and are non compliant with NI 43-101 and should not be relied upon. A qualified person has not done sufficient work to classify the historical estimates as current “mineral resources”, as such term is defined in NI 43-101 and it is uncertain whether, following further evaluation or exploration work, the historical estimates will be able to report as mineral resources in accordance with NI 43-101. Capstone has not done sufficient work to classify the historical estimate as current mineral resources and is not treating the historical estimate as current mineral resources. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. Mineral Resources reported using a cut-off grade of 0.2% with further economic extraction parameters outlined below. Mineral Resources reported by category; based on average spacing of drillholes and levels of confidence in the grade estimation. There are no more recent estimates or data available to Capstone. The Sierra Norte deposit will require further evaluation including drilling to verify the historical estimate as current mineral resources. Investors are cautioned not to place undue reliance on the historical estimates contained in this news release. Economic Parameters for Mineral Resources: Copper price: $3.00/lb Mining cost: $1.69/t Processing Sulphide recovery: 91% Sulphide processing cost: $7.26/t Oxide (heap) recovery: 60% Oxide (heap) processing cost: $8.12/t Oxide (SX-EW) processing cost: $0.30/lb Selling Costs Concentrates: $0.41/lb Cathodes: $0.04/lb (1) The total consideration is satisfied by the issuance of 2,034,970 Capstone shares at a deemed value of C$15.77/share, being the volume-weighted average closing price of Capstone’s common shares for the 10 trading days ending two business days before closing of the Transaction, net of applicable withholding taxes. (2) See Figure 3 for the Inferred Mineral Resource Estimate for San Pietro.See Figure 4 for the Estimated Mineral Reserves & Mineral Resources for Mantoverde and Santo Domingo. See Figure 5 for the Historical Mineral Resource Estimate for Sierra Norte. About Capstone Copper Corp. Capstone Copper Corp. is an Americas-focused copper mining company headquartered in Vancouver, Canada. Capstone’s operating portfolio of assets includes the Pinto Valley copper mine located in Arizona, USA, the Cozamin copper-silver mine located in Zacatecas, Mexico, the Mantos Blancos copper-silver mine located in the Antofagasta region, Chile, and the Mantoverde copper-gold mine, located in the Atacama region, Chile. Capstone’s growth pipeline includes the fully permitted Santo Domingo copper-iron-gold project, located approximately 35 kilometres northeast of Mantoverde in the Atacama region, Chile, as well as a portfolio of exploration properties in the Americas. Capstone Copper’s strategy is to unlock transformational copper production growth while executing on cost and operational improvements through innovation, optimization and safe and responsible production throughout our portfolio of assets. We focus on profitability and disciplined capital allocation to surface stakeholder value. We are committed to creating a positive impact in the lives of our people and local communities, while delivering compelling returns to investors by responsibly producing copper to meet the world’s growing needs. Further information is available at www.capstonecopper.com CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS This document may contain “forward-looking information” within the meaning of Canadian securities legislation and “forward-looking statements” within the meaning of the United States Private Securities Litigation Reform Act of 1995 (collectively, “forward-looking statements”). These forward-looking statements are made as of the date of this document and the Company does not intend, and does not assume any obligation, to update these forward-looking statements, except as required under applicable securities legislation. Forward-looking statements in this news release include statements regarding Capstone’s plans to integrate San Pietro into its district exploration activities; the exploration potential of San Pietro; potential resource growth; potential use of existing or planned infrastructure; potential operational synergies; possible future processing of mineralized material in the district; and the timing, scope and result of further drilling, data verification, technical studies, permitting and investment decisions. Forward-looking statements are based on assumptions that Capstone considers reasonable as of the date of this news release, including assumptions regarding the accuracy and completeness of information provided by the prior owner; the ability to obtain required permits and approvals; the availability of personnel, equipment, financing and infrastructure; commodity prices, exchange rates and input costs; and the results of future exploration, drilling, metallurgical testing and technical studies. Forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause actual results to differ materially, including risks relating to the accuracy or verification of historical information; exploration and geological uncertainty; the inability to convert the historical estimate into a current mineral resource or any mineral resource into a mineral reserve; changes in commodity prices, exchange rates and costs; permitting, environmental, social, title and regulatory risks; access to infrastructure; integration of acquired assets; and the other risks described in Capstone’s continuous disclosure filings available on SEDAR+. There can be no assurance that forward-looking statements will prove accurate. Readers should not place undue reliance on forward-looking statements. Except as required by applicable securities law, Capstone disclaims any intention or obligation to update or revise forward-looking statements. COMPLIANCE WITH NI 43-101 Unless otherwise indicated, Capstone Copper has prepared the technical information in this document (“Technical Information”) based on information contained in the technical reports, Annual Information Form and news releases (collectively the “Disclosure Documents”) available under Capstone Copper’s company profile on SEDAR+ at www.sedarplus.ca. Each Disclosure Document was prepared by or under the supervision of a qualified person (a “Qualified Person”) as defined in National Instrument 43-101 – Standards of Disclosure for Mineral Projects of the Canadian Securities Administrators (“NI 43-101”). Readers are encouraged to review the full text of the Disclosure Documents which qualifies the Technical Information. Readers are advised that Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. The Disclosure Documents are each intended to be read as a whole, and sections should not be read or relied upon out of context. The Technical Information is subject to the assumptions and qualifications contained in the Disclosure Documents. Disclosure Documents include the National Instrument 43-101 technical reports titled “Santo Domingo Project, NI 43-101 Technical Report and Feasibility Study Update, Atacama Region, Chile” effective July 31, 2024 and "Mantoverde Mine NI 43-101 Technical Report and Feasibility Study / Atacama Region, Chile", effective July 1, 2024. The disclosure of Scientific and Technical Information in this document was reviewed and approved by Peter Amelunxen, P.Eng., Senior Vice President, Technical Services (technical information related to project updates at Santo Domingo, Mineral Resources and Mineral Reserves at Mantoverde and Mineral Resources at San Pietro), a Qualified Person under NI 43-101. View source version on businesswire.com: https://www.businesswire.com/news/home/20260831848151/en/ Contacts: Daniel Sampieri, Vice President, Investor Relations 437-788-1767 [email protected] Michael Slifirski, Director, Investor Relations, APAC Region 61-412-251-818 [email protected] Claire Stirling, Manager, Investor Relations 416-831-8908 [email protected] Source: Capstone Copper Corp.