Viuda Sampling Indicates Increased Mineralisation

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce an update on exploration mapping and rock chip sampling at the Viuda Negra prospect ("Viuda"), part of the Company's Especularita Project.

Highlights:

• 223 rock and channel chip samples define Au-Ag-Cu mineralisation at Viuda Negra over 500 x 700 m
• High-grade Ag-Cu in outcropping epithermal silica ledges up to 186g/t Ag and 1.4% Cu
• Mapping extends intermediate argillic alteration zone 800m further south of 2025 scout drilling
• Results indicate system is open to the west and south beneath gravel cover
• Planning and permitting for drilling at Viuda are in progress
• GSC holds rights to own 100% of the Viuda prospect

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "The discovery by GSC of porphyry gold mineralisation in scout drilling at Viuda Negra last year was a significant milestone for the Company, identifying broad intervals of low-grade gold-copper associated with Maricunga-style porphyry quartz-vein stockworks. The shallow scout drilling targeted outcrops of epithermal-style alteration with anomalous gold and silver.

"These results build on last year's scout drilling through further rock and channel chip sampling, indicating that the mineralised system is significantly expanded to an area covering some 500 x 700 metres. Importantly, the system remains open to the west and south, where the mineralisation appears to extend beneath shallow colluvial cover.

"The Viuda Negra gold discovery is the first reported occurrence of Maricunga-style porphyry gold mineralisation within the coastal metallogenic belt of Chile, which is very significant given the potential scale of this deposit style, making it an exciting exploration target. Planning and permitting for the next phase of exploration drilling at Viuda Negra is now underway and is likely to include a combination of RC and diamond drilling."

Viuda prospect:

GSC's Viuda porphyry gold-copper prospect is located 20 kilometres ("km") to the southwest of the high-grade Cu-Ag prospect at Cerro Negro and is situated within the Especularita Project (Figure 1). The prospect is defined by a distinctive "bowl-shaped" caldera measuring 2km in diameter and comprising phyllic to advanced argillic altered intrusive rocks enclosed by propylitic altered andesitic volcano-sedimentary units (Figure 2).

The Especularita project is situated 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, Altar and El Pachon (Figure 1).

Figure 2: The Viuda prospect comprises a "bowl-shaped" remnant caldera feature comprising light-coloured phyllic to intermediate argillic altered intrusives and volcano sedimentary units enclosed by dark propylitic-altered andesitic volcanic rocks.

Mapping and Sampling at Viuda Negra Au-Ag-Cu prospect:

Exploration mapping and sampling has continued at Viuda Negra in response to the Company's discovery of Maricunga-style porphyry gold mineralisation in scout drilling, including assay results of 73m at 0.14g/t Au, 0.1% Cu (VNE25-DD002) and 121m at 0.11g/t Au (VNE25-DD004). The low-grade gold mineralisation is associated with distinctive Maricunga-style banded quartz-vein stockworks, however, within these intervals higher gold grades are intersected where vein densities increase (6.7m at 0.39g/t Au in VNE25-DD004)1.

Interpretation of the scout drilling results suggested that the gold mineralisation was potentially vectoring towards the southwest. Subsequent exploration to confirm the analysis, including mapping and sampling, comprising 223 rock and channel chip samples, now defines anomalous Au-Ag-Cu mineralisation extending southward and covering an area of approximately 500 x 700m (Figure 23). Outcrop exposed in track-cuttings at the site of VNE25-DD004 resulted in a channel chip result of 11m of 0.24g/t Au and 716ppm Cu, confirming that mineralisation extends further to the west and south from the original drilling (Figure 4). This has the potential to continue under shallow colluvial cover, potentially further extending the mineralised zone.

The anomalous Au-Ag-Cu mineralisation is hosted in phyllic to intermediate argillic alteration (sericite-quartz-clay-pyrite) of intrusive and volcanic tocks, which extends further south up to 800m from the mineralisation intersected in drilling.

Figure 3: Rock and channel chip sampling at Viuda Negra defines anomalous epithermal style Au-Ag-Cu mineralisation over a 500 x 700m area.

Figure 4: Summary map of gold rock chip and channel chip results at Viuda Negra prospect, indicating exploration vector to the southwest beneath colluvium cover.

Next Steps at Especularita:

Planning and permitting for the next phase of drilling at Viuda Negra is now underway, aimed at targeting mineralisation extending to the southwest beneath shallow cover.

Similarly, at Cerro Negro, mapping and sampling are ongoing at the Monolith target to assist with defining drill targets for drilling. In addition, a new IP survey is being planned to infill and extend the previous survey at Cerro Negro, which was very successful at identifying mineralisation along the Mostaza Fault Zone ("MFZ"). The new survey will infill the original survey, plus extend coverage toward the east to cover the Monolith zone and to the west to cover hanging-wall mineralisation to the MFZ. Soil sampling and ASD spectral sampling have commenced across the portion of the La Colorada lithocap associated with the Cerro Negro prospect.

The Company is awaiting results for its metallurgical test work on high-grade core samples from Phase I and II drill programmes at Mostaza, Cerro Negro and will report these in due course

References:

• RNS 4145X (01 Sep 2025): Results of Scout Drilling at Viuda Negra.

Forward Looking and Cautionary Statements