Announcement PDF RNS Number : 0134U Great Southern Copper PLC 09 September 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 September 2026 Great Southern Copper plc ("GSC" or the "Company") Induced Polarisation - Resistivity Survey Commences at Cerro Negro Prospect Results to assist targeting of Phase IV drilling Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that its in-fill and extensional induced polarisation (IP) geophysics survey has commenced at the Cerro Negro prospect, part of the Especularita Project. Highlights: · Geophysics survey comprises 5 lines of IP-Resistivity for a total of up to 6 line kilometres · Survey designed to infill previous broad-spaced exploration survey to provide 3D anomaly drill targeting · Previous survey to be extended to the east to cover Monolith Ag-Cu exploration target · Line extensions to the west target potential mineralisation in the hangingwall to the Mostaza Fault Zone · Results to assist with final targeting of the Phase IV drilling programme · GSC holds rights to own 100% of the Cerro Negro prospect · Prospect located at low elevation with excellent access to infrastructure and mining services and along trend of major copper deposits including Los Pelambres, Altar and El Pachon. Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "We are excited to have this survey underway as it is another important test of the potential to expand the known mineralisation at Cerro Negro. In particular, this survey is a key test of the Monolith zone which exhibits Cu-Ag mineralisation identified in outcrop over a 700x400m area that is very similar in character to the high-grade Cu-Ag mineralisation discovered below the Mostaza pit. Establishing a link between the two mineralised centres is a critical step in further understanding the architecture of the larger system and will provide important guidance for the exploration drilling of Phase IV at Cerro Negro. "Planning and permitting for Phase IV drilling at Cerro Negro is at an advanced stage and we look forward to announcing the start of drilling soon." Cerro Negro Prospect: In February 2025 GSC discovered high-grade Cu-Ag mineralisation beneath the historic Mostaza mine workings at its Cerro Negro prospect1 which is situated at the eastern margin of the Company's Especularita project (Figure 1). The Especularita Project is located at low altitude within the Cretaceous-age coastal metallogenic belt, within a northwest-southeast trending structural lineament that links the project with notable large-scale porphyry Cu-Au mines, and projects including Los Pelambres mine, Altar and El Pachon (Figure 1). Figure 1: GSC's Especularita project is located at low altitude within the coastal metallogenic belt of northern Chile and within 50km radius of over 50Mt of contained copper metal defined in mines and advanced projects. Induced Polarisation Survey: Work has commenced on five new lines of pole-dipole IP - resistivity planned to infill and extend GSC's previous survey completed in June 20252 (Figure 2). The previous survey delineated a prominent IP chargeability anomaly coincident with the Mostaza Fault Zone and extending over a strike length of 2km north-south. Subsequent scout RC drill testing of the anomaly successfully intersected strongly anomalous polymetallic Pb-Zn-Ag mineralisation3 . The new survey lines are planned using 40m-spaced receiver dipoles and 40m transmitter spacing consistent with the previous survey configuration. The survey is designed to characterise the chargeability and resistivity responses from near- surface to approximately 150m depth, with complimentary natural-source audiofrequency magnetotellurics ("NSAMT") providing resistivity information to nominal depths of over 300m. Acquired data will be merged with the previous survey data and processed and modelled in 2D and 3D. Next Steps: Planning and approvals for Phase IV drilling at Cerro Negro is at an advanced stage. Mapping and sampling is on-going at Cerro Negro with a focus on the Mostaza-Monolith trend with the important aim to determine how the mineralisation in these two areas may me linked. The results of the IP - Resistivity survey will play an important role in targeting maiden drill holes for the Monolith Cu-Ag mineralisation as part of the Phase IV drilling at Cerro Negro. References: 1. RNS 5182Y (26 Feb 2025): Cerro Negro Assays return 20m at 3.3% Cu and 270g/t Au 2. RNS 5859L (05 Jun 2025): Geophysics surveys commence at Cerro Negro 3. RNS 6736X (23 Mar 2025): Scout RC Drilling results for Cerro Negro Figure 2: Plan map of Cerro Negro prospect illustrating planned infill and extensional IP lines relative to the previous survey. IP crew preparing lines in the field (right). 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/y5nEQe Sam Garrett, Chief Executive Officer +44 (0) 20 7138 3204 SI Capital Limited Nick Emerson +44 (0) 1483 413500 BlytheRay Tim Blythe / Megan Ray +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. 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