Announcement PDF RNS Number : 7906Z Great Southern Copper PLC 09 April 2026 THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION AS STIPULATED UNDER THE UK VERSION OF THE MARKET ABUSE REGULATION NO 596/2014 WHICH IS PART OF ENGLISH LAW BY VIRTUE OF THE EUROPEAN (WITHDRAWAL) ACT 2018, AS AMENDED. ON PUBLICATION OF THIS ANNOUNCEMENT VIA A REGULATORY INFORMATION SERVICE, THIS INFORMATION IS CONSIDERED TO BE IN THE PUBLIC DOMAIN. 09 April 2026 Great Southern Copper plc ("GSC" or the "Company") Ground Magnetic Survey Identifies New Targets at Viuda Results highlight magnetite destructive zones coincident with porphyry-type gold-copper mineralisation and alteration Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that it has received final results from a recently completed ground magnetic survey at its Viuda porphyry gold- copper prospect ("Viuda") located within the Company's Especularita Project. Highlights: · Survey comprised 198 line-kilometres ("km") of ground magnetics across the Viuda prospect · Ground-truthing confirms magnetic-low anomalies and lineaments demonstrate strong correlation with mapped porphyry-style alteration, structures and known gold-copper mineralisation · Multiple new targets identified consistent with porphyry-style mineralisation · Large untested magnetic low anomaly identified beneath gravel cover west of Viuda Negra · Detailed mapping and sampling in progress to support interpretation and drill targeting · Planning and permitting for Phase II drilling at Viuda are in progress · Company holds options to own 100% of the Viuda prospect · Viuda and Viuda Negra are part of the Especularita Project located in Chile's coastal metallogenic belt with excellent access to infrastructure Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "The completion of the ground magnetic survey at Viuda represents an important step in advancing our understanding of this emerging porphyry-related gold-copper system. The results clearly define broad-scale geological features as well as discrete magnetic-low features that coincide with mapped alteration and known gold-copper mineralisation, reinforcing our interpretation that mineralisation is potentially related to magnetic porphyry intrusives and associated enveloping zones of magnetite-destructive alteration. "Earlier reported exploration by GSC at Viuda identified Maricunga-style porphyry gold mineralisation which has been confirmed in subsequent drilling with broad zones of gold and copper intersected which is indicative of the potential for a large-scale gold-copper porphyry system similar to those occurring in the Maricunga Belt of northern Chile. Importantly, the magnetic data provides a clear vector towards potential higher-grade centres within the system. Integration of the geophysics with ongoing detailed mapping and surface sampling will directly support refined drill targeting as we progress toward a Phase II drilling programme anticipated in Q2 2026. We look forward to updating shareholders as this work continues." Ground Magnetic Survey: Final processed results have been received for a 198 line-kilometre ground magnetic survey covering approximately 6 square kilometres ("km2 ")of the Viuda prospect (Figure 1), including Viuda Negra, where previous rock chip sampling and scout drilling discovered a mineralised porphyry gold system1,2 . High-resolution ground magnetic data were acquired by Southern Rock Geophysics on a nominal 50 metre ("m") line spacing and processed to generate Total Magnetic Intensity ("TMI"), Reduced-to-Pole ("RTP"), Analytical Signal of the Vertical Integral ("ASVI") and Magnetisation Vector Inversion ("MVI") products. ExploreGeo of Australia provided additional specialist processing and interpretation. Figure 1: Location of Viuda prospect and the Especularita Project, Chile. The project is located at low elevation within the coastal metallogenic belt and along trend of significant mines and projects in development. Survey Results and Interpretation: Preliminary interpretation of the Viuda ground magnetic data by consulting firm ExploreGeo of Australia has identified magnetic features, anomalies and lineaments that demonstrate a strong spatial correlation with mapped alteration, structures and known gold-copper mineralisation. The prospect is dominated by a broad circular region of magnetic low, approximately 2km in diameter, which correlates closely with the distinctive colour anomaly that defines the Viuda prospect, and is associated with broad-scale magnetite-destructive pyrite-sericite-clay alteration (Figure 2). Within the broad low discrete magnetic highs, where buried, have the potential to represent mineralising intrusives. At Viuda Negra, gold-copper mineralisation mapped at surface and intersected in drilling is spatially coincident with a northwest-trending magnetic low interpreted to represent magnetite-destructive clay alteration. The magnetic low extends approximately 500m to both the NW and SE of existing drilling, indicating potential for mineralisation to extend beyond currently tested areas. Field mapping and sampling of these areas are in progress. Immediately east of Viuda Negra, a discrete magnetic high anomaly crops out as a magnetic post-mineral intrusive. In the area of scout RC drilling, gold-copper mineralisation is spatially associated with the margin of a discrete magnetic high interpreted to represent magnetite-albite-chlorite altered diorite intrusive (Figure 2). This magnetic body remains untested by drilling. West of the outcropping Viuda Negra mineralisation, a large northwest-trending magnetic low, measuring approximately 1.8 km by 0.5 km, with a magnetic signature comparable to the known mineralisation and alteration at Viuda Negra is buried by shallow gravel deposits (Figure 2). Multiple intersections of NW and NE trending structures are also interpreted within this area, which represents a high-priority concealed porphyry target that remains untested by drilling. 3D inversion modelling of the magnetics also highlights the strong relationship of known gold-copper mineralisation with magnetic low regions and mapped magnetite-destructive pyrite-sericite-clay alteration (Figure 3) and further emphasises the target potential of the gravel-covered low anomalies for porphyry gold-copper type mineralisation. Interpretation of the magnetic data is ongoing and is being integrated with detailed geological mapping and surface sampling, currently in progress. This combined dataset will be used to refine the geological model and prioritise targets ahead of the next phase of drilling. Figure 2: Analytical Signal of the Vertical Integral (ASVI) image for Viuda survey showing outline of magnetite-destructive pyrite-sericite-clay alteration (black dash polygon) with GSC drill collar locations. Large central magnetic low anomaly covered by gravel is highlighted (l). Same scale Landsat8 image (clay-ser-hem) for Viuda prospect (r). Figure 3: Cross Section of the Magnetisation Vector Inversion (MVI) model across the Viuda and Viuda Negra prospects (looking to the northwest) showing drillholes and zones of interpreted magnetite-destructive alteration. Porphyry Gold-Copper Mineralisation at Viuda: Scout diamond drilling at Viuda Negra in 2025 targeted outcropping Maricunga style banded quartz veining with coincident gold-copper anomalism in rock chip samples. The holes intersected broad zones of vein alteration with anomalous gold- copper mineralisation consistent with known porphyry gold type deposits including significant intervals2 ; o DD004: 121.5m @ 0.11 g/t Au & 0.05% Cu from 6.5m, including § 6.7m @ 0.39 g/t Au & 0.12% Cu from 43.1m Maximum assay of 0.55 g/t Au o DD002: 73m @ 0.14 g/t Au & 0.1% Cu from 11m including § 14.2m @ 0.21 g/t Au & 0.11% Cu from 11m The discrete higher-grade interval in DD004 is associated with a porphyritic microdiorite intrusive phase which is over-printed by abundant banded and A-type quartz veinlets and intense, magnetite-rich potassic alteration (Figure 4). This is interpreted as an early-mineral porphyry phase and suggests that higher-grade centres may be present elsewhere within the system. The scout drilling confirms that gold and copper mineralisation is associated with stockwork and sheeted dark-banded and A- type quartz veinlets within widespread intermediate-argillic and magnetite-albite-chlorite altered diorite porphyry intrusives. The mineralisation and alteration observed at Viuda are typical of Maricunga-style gold porphyry systems (Figure 5), such as Kinross Gold's Lobo-Marte deposit (6.7Moz Au at 1.3 g/t3 ), Maricunga (4.3 Moz at 0.7 g/t4 ) and Rio2's Fenix deposit (1.77 Moz Au at 0.48 g/t Au5 ). Figure 4: Viuda Negra Prospect. Drillhole VNE25-DD004 - 57-60m. Stockwork and sheeted dark banded quartz veinlets. Assay 0.17 g/t Au. Figure 5: Viuda Negra drilling section and results (r) compared with the Caspiche porphyry Au-Cu deposit. References: 1. RNS 2553F (16 April 2025): Scout RC Drilling at Viuda 2. RNS 4145X (1 September 2025): Results of Scout Drilling at Viuda Negra 3. Kinross Gold 2024 Annual Mineral Resource and Resource Statement 4. Kinross Gold 2015 Annual Mineral Resource and Resource Statement 5. NI 43-101 Technical Report on the Feasibility Study for the Fenix Gold Project Engage with the GSC management team directly by asking questions, watching video summaries and seeing what other shareholders have to say. Navigate to our Interactive Investor hub here: https://gscplc.com/ Enquiries: Great Southern Copper plc https://gscplc.com/link/rvvabr Sam Garrett, Chief Executive Officer +44 (0) 20 7138 3204 SI Capital Limited Nick Emerson +44 (0) 1483 413500 BlytheRay Megan Ray / James Mulligan +44 (0) 20 7138 3204 GSC@blytheray.com Subscribe to our news alert service: https://gscplc.com/auth/signup Notes for Editors: About Great Southern Copper Great Southern Copper PLC is a UK-listed mineral exploration company focused on the discovery of copper-gold-silver deposits in Chile. The Company has the option to acquire mining rights to 100% of Especularita project in the under-explored coastal belt of Chile that is prospective for large scale copper-gold-silver deposits. Chile is a globally significant mining jurisdiction being the world's largest producer and exporter of copper. The Especularita Project is located in the coastal metallogenic belt of Chile which hosts significant copper mines and deposits, including Teck's Carmen de Andacollo copper mine, and boasts excellent access to infrastructure such as roads, power and ports. Significant historical small-scale and artisanal workings for both copper and gold are readily evident in the exploration project area. The coastal belt offers deposit type optionality for copper including porphyry and IOCG style deposits as well as newly recognised intrusive-related copper and gold deposits. Great Southern Copper is strategically positioned to support the global market for copper - a critical battery metal in the clean energy transition around the world. The Company is actively engaged in exploration and evaluation work programmes targeting both large tonnage, low to medium grade Cu-Au as well as high-grade Cu-Ag-Au deposits. Further information on the Company is available on the Company's website: https://gscplc.com Competent Person Statement The information in this announcement that relates to exploration results is based on and fairly represents information reviewed or compiled by Mr Sam Garrett, a Competent Person who is a Member of the Australian Institute of Geoscientists and a Fellow of the Society of Economic Geologists. Mr Garrett is the CEO and a shareholder of Great Southern Copper PLC. Mr Garrett has sufficient experience that is relevant to the styles of mineralisation and types of deposit under consideration and to the activity being undertaken to qualify as a Competent Person as defined in the 2012 Edition of the "Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves". Mr Garrett has provided his prior written consent to the inclusion in this announcement of the matters based on information in the form and context in which it appears. This announcement includes information that relates to Exploration Results prepared and first disclosed under the JORC Code (2012) and extracted from the Company's previous LSE announcements as noted, and the Company's Prospectus dated 20 December 2021. Copies of these announcements are available from the LSE Announcements page of the Company's website: www.gscplc.com. The Company confirms that it is not aware of any new information or data that materially affects the information included within the Prospectus dated 20 December 2021. Forward Looking and Cautionary Statements Some statements in this announcement regarding estimates or future events are forward-looking statements. They include indications of, and guidance on, future earnings, cash flow, costs and financial performance. Forward-looking statements include, but are not limited to, statements preceded by words such as "planned", "expected", "projected", "estimated", "may", "scheduled", "intends", "anticipates", "believes", "potential", "predict", "foresee", "proposed", "aim", "target", "opportunity", "could", "nominal", "conceptual" and similar expressions. 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