Scout RC Drilling Results

New copper discovery validates exploration model and strategy for Especularita

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce first assay results received for four of the scout RC (reverse circulation) drill holes of the recent Especularita drilling programme.

Highlights:

• Artemisa North scout RC hole RC009 tested beneath artisanal workings with oxide copper and intersected;

§ 106m @ 0.33% Cu and 42 ppm Mo, from surface, and including

§ 54m @ 0.46% Cu and 66ppm Mo, from 16m

• Disseminated and vein-hosted chalcopyrite-bornite-molybdenite mineralisation is hosted in potassic alteration and strongly indicative of porphyry copper type mineralisation
• Mineralisation is open in all directions with the hole terminated in chalcopyrite-mineralised granodiorite
• Hole RC011 at Victoria prospect also intersected broad potassic alteration including multiple narrow mineralised zones with grades up to 0.85% Cu and 0.53g/t Au
• Results confirm significant potential for large-scale porphyry copper-style mineralisation at Especularita and specifically beneath and surrounding the La Colorada lithocap
• Assay results are pending for the remaining 13 RC holes
• GSC holds rights to own 100% of the Especularita Project
• Project located at low elevation with excellent access to infrastructure and mining services and along trend of major copper mines and deposits including Los Pelambres, Altar and El Pachon

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "This outstanding result for hole RC009 has greatly exceeded our expectations for the reconnaissance drilling programme and sets the scene for a very exciting exploration campaign to follow-up this porphyry copper discovery.

"Hole RC009 targeted artisanal workings located beneath an outer remnant of the La Colorada lithocap. The hole has intersected a broad zone of porphyry copper style mineralisation with anomalous molybdenum that appears to be open in all directions. This result validates the Company's aggressive 'drill-early' exploration strategy and confirms our working model that the La Colorada lithocap has the potential to conceal large-scale porphyry copper deposits.

"This is an excellent reward for our exploration team that has worked hard and now produced three significant discoveries at Especularita in the last two years, including high-grade Cu-Ag at Mostaza and Maricunga-type porphyry gold at Viuda. As with the earlier discoveries, what is key here is that the mineralisation has been intersected from surface and is located near to the coast with excellent access to mining infrastructure and services. The discovery of porphyry copper mineralisation is an important compliment to our advanced high-grade copper-silver discovery at Cerro Negro in that it has the potential to significantly increase the global copper endowment of the project and increases our confidence in the exploration potential of the lithocap itself.

"Whilst we await the results for the final drill holes our team will immediately commence the work of detailed mapping and sampling of the hole RC009 area to prepare for follow-up geophysics surveys and drilling."

Especularita Project Overview:

The Company's 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). The exploration Project is centred upon the La Colorada lithocap, a giant high-sulphidation advanced argillic alteration system that is highly prospective for concealed porphyry copper deposits as well as other porphyry-related types of mineralisation which may occur within or marginal to the lithocap environment. These include the advanced Cerro Negro prospect, located on the eastern side of the lithocap, where the Company recently discovered high-grade Cu-Ag mineralisation beneath the old Mostaza mine workings.

Unlike the younger porphyry copper belts that make up the high Andes, the Cretaceous-age coastal metallogenic belt is notable in Chile in that it hosts multiple types of copper deposits including porphyry copper deposits (PCD), iron-oxide copper deposits (IOCG) and intrusive-related gold-copper systems (IRGS). All of these deposit types are recognised within GSC's Especularita project area.

Scout RC Drilling Programme:

Whilst the La Colorada lithocap covers a vast area (>75km2), previous work by GSC geologists has identified silica-sericite-pyrite (phyllic) alteration outcropping over large areas surrounding the lithocap suggesting that the high-sulphidation advanced argillic style alteration (La Colorada lithocap) potentially once extended to the west and south well beyond its present mapped area. This observation is significant as it allows for the potential for porphyry copper systems to occur where the lithocap has been eroded away potentially exposing the tops of porphyry copper systems.

To evaluate this idea GSC designed a "Proof-of-Concept" drill programme comprising short, broadly-spaced RC holes ("reconnaissance" or "scout" holes) spread across a number of prospects allowing the Company to rapidly and cheaply assess the potential of the targets prior to committing significant time and resources to larger more costly programmes.

A total of 17 drill holes (comprising 2,474m) were completed across four target areas on the western and southern flanks of the advanced argillic lithocap alteration including Piedras Blancas1, Artemisa North2, Victoria3 and Artemisa South4 (Figure 2). Assay results for this release are reported for RC001 and RC002 (Piedras Blancas), RC009 (Artemisa North) and RC011 (Victoria). Results for holes RC003 - RC008, RC010, and RC012 - RC017 are pending.

Figure 2: Geology and summary drill hole plan map for the scout RC programme, Especularita Project (left). Photograph (right) shows the mineralised microdiorite at Artemisa North in the foreground with black oxide copper staining and hills of the advanced argillic altered La Colorada lithocap in the background.

Artemisa North (ART26-RC009):

Drillhole RC009 was drilled at the Artemisa North target, testing beneath outcropping copper oxide mineralisation in artisanal workings (Figure 2). The hole intersected microdiorite, diorite and granodiorite intrusives exhibiting strong biotite-magnetite (potassic) alteration (Figure 3) and returning significant down-hole assay grades including:

• RC009: 106m @ 0.33% Cu and 42ppm Mo from surface (0m), including

§ 54m @ 0.46% Cu and 66ppm Mo, from 16m, and

§ 20m @ 0.57% Cu and 116ppm Mo from 16m

Mineralisation is associated with copper oxides and sulphides down to depths of approximately 54m from surface, transitioning to disseminated and veinlet-hosted chalcopyrite-bornite at depth (Figure 4). Mineralisation is hosted in all of the intrusive phases with the highest and most consistent grades associated with the microdiorite intrusive that represents a high priority target for follow up drilling (Figure 3).

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 zone3.

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 zone3.

Figure 3: Drilling cross-section for scout hole RC009 at Artemisa North with summary geology and copper grade intercepts.

Figure 4: Examples of porphyry copper type mineralisation identified in chip samples of drill hole RC009.

Victoria (VIC26-RC011):

RC011 tested the Victoria target3 (Figure 2) and intersected a microdiorite intrusive displaying strong biotite-magnetite (potassic) alteration together with localised copper mineralisation, returning down-hole assay grade intervals inlcuding:

RC011: 14m @ 0.23% Cu and 0.18 g/t Au from 6m, including

§ 2m @ 0.85% Cu and 0.48 g/t Au from 8m

And:

RC011: 2m @ 0.64% Cu and 0.14 g/t Au from 38m

The occurrence of biotite-magnetite altered microdiorite at Victoria is similar to the alteration-lithology association observed in RC009 at Artemisa North and supports the interpretation of a broad porphyry system within the outer margins of the La Colorada lithocap. Further geological and assay interpretation will be used to assess the significance of this relationship and refine future drill targeting.

Piedras Blancas (PDB26-RC001 & RC002):

Drillholes RC001 and RC002 intersected diorite and granodiorite intrusives with intense quartz-sericite-pyrite phyllic alteration and quartz-pyrite veinlets, transitioning to biotite-magnetite alteration (potassic alteration) at depth with evidence of 5 - 15% disseminated and veinlet hosted pyrite, traces of chalcopyrite and quartz veinlets. Both drillholes show anomalous Cu up to 0.13% Cu supporting the presence of porphyry style mineralisation at the prospect.

The style and intensity of alteration and mineralisation identified in holes RC001 and RC002, 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 RC drilling recently commenced at several prospects around the southern margins of the La Colorada lithocap with a view to test the prospects for evidence of porphyry copper-gold mineralisation and to provide vectors towards targets beneath the undrilled Colorada lithocap. A preliminary "Prro-of-Concept" test comprising 17 holes and 2,474m of drilling was completed across 4 prospect areas, namely Piedras Blancas, Artemisa North, Artemisa South and Victoria.

Next Steps:

Assay results are awaited for the final 13 scout RC holes in this programme which may affect the forward plans for follow-up exploration in this area. However, the results for discovery hole ART26-RC009 are highly significant and the company will immediately begin detailed mapping and sampling in the Artemisa North area to prepare for possible IP geophysics and further RC drilling.

References:

• RNS 0949B (20 April 2026): Drilling Commences with First Test of Porphyry Copper Targets at Especularita
• RNS 1366E (13 May 2026): Scout RC Drilling Commences at Artemisa North Porphyry Copper Target
• RNS 5465G (02 June 2026): Scout RC drilling commences at Victoria target
• RNS 3799I (16 June 2026): Scout RC drilling commences at Artemisa South copper-gold target

Forward Looking and Cautionary Statements