Scout Drilling Commences at Artemisa North Target

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that scout RC drilling has commenced on the Artemisa North porphyry copper target at the Especularita Project, while drilling recently completed at the nearby Piedras Blancas target has confirmed evidence of a strong porphyry copper-style alteration system.

Highlights:

Artemisa North

• Scout reverse circulation ("RC") drilling commences at Artemisa North porphyry copper prospect at the western margin of the La Colorada lithocap
• Four holes planned to target interpreted phyllic alteration system plus test beneath historical copper workings
• Rock chip geochemistry results from mine workings grade up to 1.21% Cu, 0.6g/t Au and 201ppm Mo
• Large-footprint system open under shallow cover to the north and east
• No previous drilling of the target
• GSC holds rights to own 100% of the Artemisa North target

Piedras Blancas

• Scout RC drilling completed at Piedras Blancas prospect with four holes drilled for 574 metres ("m")
• All holes successfully intersected strong porphyry type phyllic alteration with holes PBL26 RC001 and RC002 transitioning at depth to potassic alteration including 5-15% sulphide mineralisation
• Style and intensity of alteration provides proof-of-concept confirmation of a porphyry copper type setting at Piedras Blancas intersected at shallower depths than expected and further increasing prospectivity of the broader La Colorada lithocap
• Samples for all four holes at Piedras Blancas have been despatched to ALS Laboratories
• GSC holds rights to own 100% of the Piedras Blancas target

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Artemisa North is the second of four targets to be tested with scout RC drilling in the current porphyry exploration programme. This programme is focusing on targets on the western margin of the La Colorada lithocap that display geological, geochemical and spectral features that are characteristic of porphyry copper systems. In particular, we aim to confirm that large-footprint zones of leached and oxidised quartz-sericite-pyrite alteration mapped at surface may represent the "phyllic" alteration zone enveloping a copper-gold porphyry system. Our interpretation is that these prospects were once covered by the La Colorada lithocap, which has since been eroded, or partially eroded, exposing the "phyllic" alteration.

"Drilling is progressing well and, importantly, the alteration and mineralisation observed in the initial Piedras Blancas holes has provided encouraging support for our porphyry copper exploration model at La Colorada including recognition of both phyllic and potassic styles of alteration. We look forward to receiving and sharing the sample results of the drilling in due course.

"Meanwhile, exploration mapping and sampling activities are continuing at both the Cerro Negro and Viuda prospects as we prepare for the next phase of drilling across the Especularita Project."

Artemisa North Porphyry Target:

The Artemisa North prospect is located 1.5km south of the Piedras Blancas1 prospect on the western margin of the extensive La Colorada lithocap that comprises the Company's principal porphyry copper target within its flagship Especularita project (Figure 1). 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).

Mapping and sampling at Artemisa North has defined a broad zone (>1 km2) of quartz-sericite-pyrite "phyllic" alteration and stockworking confirmed by ASD spectrography. The phyllic alteration zones upwards to quartz-alunite "advanced argillic" alteration on the surrounding hilltops that is interpreted to represent a distal remnant of the La Colorada lithocap alteration (Figure 2). Despite intense oxidation and leaching, rock chip and soil samples define local anomalies in Cu and Mo, and abundant green and black Cu-oxides are observed in historical artisanal mines exposed on the western and eastern margins of the phyllic zone.

The alteration zone remains open under shallow cover to the east towards the La Colorada lithocap, and to the north where it is interpreted to merge with the Piedras Blancas alteration zone.

Piedras Blancas Porphyry Target:

Drilling at the Piedras Blancas target has been completed with four scout RC holes drilled for a total of 574m. All holes intersected strong pervasive quartz-sericite-pyrite alteration providing proof-of-concept evidence for porphyry copper type phyllic alteration to depths of up to 120m from surface. The phyllic alteration comprises up to 5 - 10% disseminated and veinlet hosted pyrite mineralisation (Figure 3).

Holes RC001 and RC002 transitioned at depth into biotite-altered "potassic" alteration with 5 - 15% disseminated and veinlet hosted pyrite, traces of chalcopyrite and quartz veinlets.

The style and intensity of alteration and mineralisation identified in holes PBL26 RC001 and 002, in particular the potassic alteration, confirm that a porphyry copper type setting has been identified at Piedras Blancas at depths shallower than expected. These results further confirm and enhance the potential of the La Colorada lithocap to host one or more porphyry copper type systems at reasonable depths from surface. Further work will now focus on vectoring to the possible copper-rich core of the systems.

Scout RC Drill Programme and Sampling:

Scout reverse circulation (RC) drilling recently commenced at Artemisa North with a view to test the prospect for evidence of porphyry copper-gold mineralisation and to provide vectors towards targets beneath the undrilled Colorada lithocap. A preliminary test comprising up to 1000m of drilling in at least four scout RC holes is now underway to assess the alteration and mineralisation.

Figure 2: Geology map of the Piedras Blancas and Artemisa North prospects illustrating quartz-sericite-pyrite "phyllic" alteration zone and local artisanal mine locations where copper and gold were recovered from oxidised fracture stockwork zones.

Figure 3: Chip samples from Piedras Blancas drill holes RC001-004 demonstrating features of porphyry type alteration including; quart-sulphide veinlets overprinting quartz-sericite-pyrite (phyllic) altered rock (top left), coarse sulphide in quartz-sericite-chlorite-pyrite altered rock (top right), quartz veinlet hosting coarse pyrite+chalcopyrite (bottom left), disseminated chalcopyrite mineralisation in potassic altered rock (bottom right).

Next Steps at Especularita:

Following the completion of the Artemisa North scout RC drilling programme, the rig will proceed to the Artemisa South and Victoria prospects to complete similar drill tests targeting porphyry-related copper mineralisation.

Final results are awaited for Mostaza metallurgical test work conducted on Phase I and II high-grade core samples. Planning and permitting for Phase IV drilling at Mostaza are in progress.

Geophysics surveys are being planned for both the Cerro Negro prospect (extension of 2025 IP survey) and the La Colorada lithocap (AMT), anticipated to commence in May 2026.

Detailed prospect-scale mapping and sampling are continuing at the Viuda and Cerro Negro prospects. New results from this ongoing work, together with results of the planned geophysics surveys, will direct targeting for the next phase of drilling at both Cerro Negro and Viuda.

References:

• RNS 0948B (20 April 2026): Drilling commences on porphyry copper targets

Forward Looking and Cautionary Statements