Announcement PDF RNS Number : 9584U Great Southern Copper PLC 12 August 2025 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. 12 August 2025 Great Southern Copper plc ("GSC" or the "Company") Final IP Geophysical Results Define Multiple New Drill Targets at Cerro Negro Results correlate strongly with geology and geochemistry defining significant mineralised structure Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce final results for its pole-dipole IP ("PDIP") and audio magneto-telluric ("AMT") surveys at the Cerro Negro project which confirm potential for a significant Cu-Ag mineralised trend south of the Mostaza mine. Highlights: · Coincident PDIP chargeability and resistivity anomalies at Mostaza mine (Line 1) correlate strongly with high-grade Cu-Ag mineralisation identified at depth in previous drilling · Results confirm structural complexity of the Mostaza deposit · · · · · · Anomalies on Lines 2-5 are consistent with earlier reported gradient array IP anomalies1 and geochemistry results2 defining a 2.5km mineralised trend south of the Mostaza mine 2D inversion modelling of AMT results identifies targeted north-south structural trend Geophysical results identify priority untested targets for Phase III drilling over 2.5km trend Planning for Phase III exploration drilling advanced with expected start date late August GSC holds option to own 100% of the Cerro Negro prospect, including the Mostaza mine Prospect located at low elevation with excellent access to infrastructure and mining services Sam Garrett, Chief Executive Officer of Great Southern Copper, said:"These exciting pole-dipole IP results clearly identify the high-grade sulphide mineralisation drilled by GSC beneath the historical Mostaza mine, and provide compelling targeting vectors for our upcoming drilling campaign designed to explore the extensions of the mineralised system to the south along the Mostaza Fault trend. Importantly, these results also confirm the post-depositional structural complexity of this deposit and suggest geophysics will be a critical tool to assist with directing future drill programmes and ultimately understanding the complex architecture of the deposit. "The geophysical anomalies confirm and correlate with earlier geochemistry and gradient array IP results indicating potential for a mineral trend of up to 2.5km south of the Mostaza mine which remains open. "These results significantly enhance the potential of the project and represent a compelling opportunity for discovery in our upcoming Phase III programme which we anticipate starting before the end of August, subject to rig availability." Pole-Dipole IP (PDIP) / Resistivity Survey Results: Details of the physical parameters of the geophysics surveys, conducted by Southern Rock Geophysics SpA, at Cerro Negro were reported previously1 including results of the gradient array IP survey. GSC has now completed interpretation of the results from its pole-dipole IP / Resistivity and AMT surveys. Line 1 was designed as a control line as it tests the known Mostaza Cu-Ag mineralisation adjacent to the pit. Line 2 tests known mineralisation at surface and Lines 3-5 are exploration lines1 designed to confirm surface exploration results and assist with follow-up exploration drill targeting. The high-grade Cu-Ag mineralisation intersected in GSC's previous drilling3,4,5,6 at the Mostaza mine correlates closely with the upper margin of a discrete coincident chargeability and resistivity anomaly in the 2D inversion model for Line 1. Sulphide mineralisation zones identified in drilling consistently occurs at the zone of highest contrast on the top side of the anomaly (see Figure 1, 2). The Line 1 anomaly dips approximately 50° NW, consistent with the interpreted geometry of the Cu-Ag mineralised body intersected in diamond drilling. Moderate chargeability values, up to 15 milliseconds ("ms"), are consistent with the low total-sulphide but high-grade assemblage of chalcocite, bornite and digenite mineralisation. The chargeability feature is coincident with a high-resistivity anomaly (Figure 2) in both the PDIP and AMT inversions (up to 800 ohm-metres), interpreted to reflect silicification and late quartz vein-crackle alteration associated with the mineralisation. The Line 1 chargeability-resistivity anomaly provides a clear geophysical signature aligned with the known Cu-Ag mineralisation drilled at Mostaza and further provides a clear vector for targeting similar anomalies identified both down-dip, up-dip and laterally along strike to the south on subsequent test-lines 2 - 5. The Mostaza Fault, interpreted as a potentially significant controlling structure for mineralisation along the Cerro Negro trend, is recognised in the geophysics on all lines as a pronounced steeply west-dipping break in both chargeability (PDIP) and resistivity (PDIP and AMT), closely correlated with surface mapping and drillcore observations (Figures 3, 4). On Line 1, the interpreted Mostaza Fault appears to structurally dislocate the chargeability-resistivity anomaly suggesting the anomaly to the east of the fault has potentially represents a downthrown or is a separate, untested lens of mineralisation. With values comparable to the drill-tested part of the anomaly (up to 12 ms) dips approximately 50° north-west, mirroring the geometry of the previously defined and drill-tested mineralisation (Figure 1, 2). At surface, the chargeability feature potentially correlates with highly anomalous silver and copper assays from the previously mapped Lens 5. At surface the lens is intensely leached and oxidised, with rock chip assays up to 86.3 g/t Ag and 0.66% Cu indicating the potential for higher grade sulphide mineralisation at depth which is yet to be tested with drilling. Audio Frequency Magneto-telluric (AMT) Results: The AMT results confirm broader geologic trends with 3D inversion modelling clearly identifying a resistive domain to the east correlating with dacitic dome rocks in apparent faulted contact (Mostaza Fault) with low-resistive volcanic units to the west (Figure 5). Strong silicic alteration and silica-magnetite brecciation mapped along the fault potentially enhance the resistive contact evident in the modelling. On all the survey lines, there is a consistent shallow west-dipping contact between an overlying wedge or layer of relatively low resistivity overlying higher resistivities in the western part of each section. This contact, as described for the PDIP result on Line 1, may represent a prospective location for the development of sulphide mineralization associated with silicification away from the perhaps structural complexity of the Mostaza Fault Zone. Figure 1:Cerro Negro Prospect, Mostaza Mine: Cross section for 2D inversion model of chargeability for PDIP Line 1. Mostaza high-grade Cu-Ag drill intercepts coincide closely with upper margin of the chargeability anomaly (left side of Mostaza Fault). Similar anomalies to the right side of the fault are untested by drilling but demonstrate evidence of mineralisation at surface. Figure 2:Cerro Negro Prospect, Mostaza Mine: Cross section for 2D inversion model of resistivity for PDIP Line 1. Resistivity and chargeability anomalies are coincident confirming mineralisation associated with highly resistive silicified alteration. (note: for resistivity, blue colours are high). Similarly, the resistivity confirms structural complexity with dislocated anomalies and potential untested anomalies upslope of the mine. Figure 3:Cerro Negro Prospect, Mostaza Trend: Oblique view looking to the NE showing the 2D inversion of PDIP chargeability for all 5 lines together with superimposed surface geochemistry. Figure 4:Cerro Negro Prospect, Mostaza Trend: Oblique view looking to the NE showing the 2D inversion of PDIP resistivity for all 5 lines together with superimposed surface geochemistry. The resistivity response from line to line is similar and interpreted to reflect similar geology to that observed at the Mostaza Mine (Line 1). Note: Blue colours represents high resistivity. Figure 5:Cerro Negro prospect. 3D inversion modelling of AMT data highlights highly resistive rocks to the east of the Mostaza Fault Zone (dacitic dome rocks) in structural contact with less resistive volcanic rocks to the west of the MFZ. Next Steps - Multiple Undrilled Targets Identified Along Trend: The Cerro Negro geophysics surveys have identified several discrete chargeability-resistivity anomalies along a 2.5 km trend south of the Mostaza Mine, defined by survey Lines 2 through 5. These anomalies show similar geophysical characteristics to the known Cu-Ag sulphide mineralisation identified on Line 1-moderate to high chargeability (up to 12-14 ms) coincident with high resistivity-suggesting potential for sulphide-bearing, silicified bodies at depth. See Figures 3 and 4. Each of these targets coincides with mapped zones of alteration and anomalous surface Cu-Ag geochemistry. All of the targets are untested by drilling. Together, they represent a compelling cluster of high-priority targets that may reflect a network of stacked or sub-parallel mineralised bodies along the broader Mostaza Fault trend. Integration of these geophysical results with geological mapping and surface assays is ongoing and will inform final drill planning for Phase III exploration. References: 1. RNS 8981Q (14 July 2025): Gradient Array IP Anomaly Extends for 2.5km S of Mostaza Cu-Ag Mine 2. RNS 3120K (31 Oct 2024): Cerro Negro Exploration Results Up To 4.64% Cu and 177ppm Ag 3. RNS 5182Y (26 Feb 2025): Cerro Negro assays return 20m of 3.3% Cu, 270g/t Ag 4. RNS 9022A (17 Mar 2025): Exceptional results confirm potential of Mostaza 5. RNS 8896D (07 Apr 2025): Further exceptional assay results from Mostaza 6. RNS 1375O (24 June 2025):Exceptional Drilling Results Continue at Mostaza Enquiries: Great Southern Copper plc Sam Garrett, Chief Executive Officer c/o BlytheRay +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 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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