Scout RC Drilling Campaign Completed

Exploration Update

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that it has completed its first scout RC drilling programme at the Especularita Project targeting large-scale porphyry copper systems.

Highlights:

• Seventeen scout RC holes completed for a total of 2,474 metres ("m") drilled
• The La Colorada advanced argillic lithocap is vast in size and interpreted to represent the upper high-sulphidation levels of an alteration system that is potentially overlying porphyry-related copper mineralisation
• Drilling designed to assist with geological interpretation in areas surrounding the advanced argillic lithocap where the Company believes the lithocap has been eroded potentially exposing underlying porphyry-style alteration at surface
• Porphyry copper type alteration is evidenced in the drilling at Piedras Blancas, Artemisa North and Victoria
• First assay results are expected within the next 2-4 weeks
• GSC holds rights to own 100% of the Especularita project
• Prospect located at low elevation with excellent access to infrastructure and mining services and along trend of more than 85 million tonnes of contained copper hosted in major deposits including Los Pelambres, Altar and El Pachon

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "We are pleased to have completed our first drilling test of the flanking margins of the giant lithocap alteration system at Especularita. This programme is important because it will allow us to vector future drilling within the lithocap to target areas that have the most potential to host copper and gold mineralisation. The lithocap covers a vast area of over 75km2, however, we suspect that it was originally much larger and has since been eroded - potentially exposing porphyry copper style alteration at the present surface.

"The RC drilling has proven highly effective in efficiently testing four prospect targets, and the results from this programme already suggest that we are seeing porphyry-related phyllic alteration at surface at Piedras Blancas and Artemisa North and, more importantly, potassic alteration at shallow depths below that.

"Elsewhere, exploration is continuing on multiple fronts across the project to enable the momentum of drilling work to continue. In particular, mapping and sampling at both the Cerro Negro and Viuda prospects is ongoing and aimed to assist with planning for the next phases of exploration drilling in those locations."

Scout RC Drilling at Especularita:

The scout RC drilling programme at Especularita targeted prospects along the western and southern margins of the La Colorada lithocap (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).

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 50 million tonnes of contained copper metal defined in mines and advanced projects.

A total of 17 drill holes (comprising 2,474m) have been 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).

Drillholes at Piedras Blancas and Artemisa North (RC001 - RC009) intersected a complex of diorites and locally porphyritic microdiorites with widespread strong to intense magnetite-biotite-pyrite alteration overprinted by zones of strong to intense chlorite-sericite alteration with over 10% disseminated pyrite and local quartz and pyrite stockwork veinlets. Importantly, this alteration is consistent with the outer phyllic alteration zone (or shell) in a porphyry copper type system (Figure 3). Of special note is the occurrence of porphyry-copper style potassic alteration, defined by hydrothermal biotite with over 10% disseminated pyrite and minor chalcopyrite and quartz veinlets, intersected in the bottoms of holes RC001 at Piedras Blancas and RC008 at Artemisa North. These two holes lie furthest to the east and were drilled directed towards the lithocap, beneath zones of outcropping quartz-sericite stockwork veining, suggesting the system may be improving in this direction. Importantly, this potassic alteration was intercepted within a hundred metres of surface suggesting that the system may be telescoped and the porphyry centre could potentially be close to surface.

Drilling at Victoria and Artemisa South (RC010 to RC017) was also dominated by variable magnetite-biotite alteration developed in hornfelsed volcanics (Victoria) and diorites to granodiorites (Artemisa South). However, phyllic-style pyrite-sericite-chlorite alteration is less intense than the northern areas and seems to be more structurally controlled, which is consistent with the mineralisation observed at surface as vein swarms of carbonate-quartz-sulphide and/or quartz-sericite-chlorite plus sulphides. The intensity of veining and presence of Cu-oxide occurrences increases generally northwards towards the lithocap, further suggesting that the source of the fluids lies to the north and beneath the advanced argillic alteration that defines the La Colorada lithocap.

Figure 2: Geology and summary drill hole plan map for the scout RC programme, Especularita Project.

La Colorada Lithocap:

Where preserved, lithocaps overlie and conceal the location and source of potential porphyry Cu mineralisation at depth (Figure 3). They are formed by hot acidic fluids ascending to the surface from the porphyry intrusion below and the subsequent interactions of those fluids with the enclosing wall rocks. Interaction of the rising fluids with porous volcanic rocks, for example, typically results in a laterally extensive, flat-lying "blanket" of silica-mica-clay-pyrite alteration (defined as advanced argillic alteration) above the porphyry system below. Uplift, weathering and exposure of the pyritic-rich alteration to oxidising surface waters creates highly acidic fluid conditions which then acts to strip (or "leach") metals and other minerals from the altered rock resulting in a hard, silica-dominant and highly resistive cap-rock overlying the porphyry alteration system.

The lithocap may also itself be mineralised - with gold-silver-copper deposits not uncommon within the advanced argillic alteration zones. However, due to acid-leaching, the oxidised surface areas of the silica-rich lithocaps are typically barren and chemically inert to depths of up to several hundreds of meters depending upon the weathering and erosion profile which, as a result, can mask the presence of underlying high-sulphidation and porphyry copper mineralisation.

Figure 3 below is a summary model of an idealised porphyry copper system that incorporates features that the GSC exploration team believes are significant to the Especularita project and, specifically, where the Company's prospects may occur within the system. Surrounding the vertically-continuous porphyry intrusion(s) the alteration system forms typically as overlapping shell-like carapaces zoning outward from the mineralising porphyry intrusion as;

• Potassic (magnetite-Kspar) -> phyllic (sericite-chlorite-pyrite) -> propylitic (epidote) alteration shells
• Advanced argillic (qtz-al-kaol-pyro-dic) forms near-surface blanket. High pyrite produces acid leaching
• High sulphidation Au-Ag+Cu can occur at base of lithocap below the acid-leached weathering zone
• Intermediate sulphidation Cu-Pb-Zn-Ag related to late dacitic domes
• Porphyry copper grades increase inwards towards the potassic core

Figure 3: Geology model illustrating typical Chilean type porphyry copper systems such as Especularita (Modified from: Sillitoe, 2010, Porphyry Copper Systems: Economic Geology, v. 105 p. 3-41). GSC's main prospects are referenced relative to their interpreted respective locations within the broader porphyry system.

GSC's La Colorada advanced argillic lithocap alteration system is vast, measuring over 75km2 in area, and to date the Company has explored less than 25% of the total prospective area. In order to efficiently vector exploration focus towards the hidden porphyry copper zones the Company is undertaking extensive and detailed spectral and low-detection geochemistry surveys to map the temperature-pH mineralogy of the alteration minerals which provides clues to the hot acidic fluid pathways leading down-ward to the porphyry copper mineralisation below the lithocap. This work, combined with the recent AMT surveys and scout RC drilling results will be critical in planning the next phase of exploration drilling of the lithocap to target both high-sulphidation Au-Ag-Cu and porphyry Cu mineralisation.

Scout RC Drill Programme and Sampling:

Exploration Update:

Geology and geochemical assay results for the scout RC drilling programme will be used to vector the next phase of exploration drilling at the La Colorada lithocap. First assay results are expected within the next 2-4 weeks.

Final leach test results are pending from the Mostaza metallurgical test work conducted on Phase I and II high-grade drill core samples.

Planning for extensions to the Cerro Negro IP survey is also underway and anticipated to commence during July-August 2026. Results of the IP survey will guide targeting for Phase IV drilling at Cerro Negro, including Mostaza.

Detailed prospect-scale mapping and sampling are continuing at both 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 Viuda and Cerro Negro.

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