Drilling Commences on Porphyry Copper Targets

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 at the Piedras Blancas (White Stones) prospect located on the western margin of the La Colorada lithocap, in the Especularita project ("Especularita").

Highlights:

• Drilling to test porphyry Cu target at Piedras Blancas with initial three scout reverse circulation ("RC") holes
• Holes targeting silica-sericite-pyrite altered rocks with overprinting silica-pyrite stockwork alteration indicative of porphyry copper-related phyllic alteration zone
• Target outcrops over 1km in diameter but extends under gravel cover to east and south
• Anomalous molybdenum up to 49 ppm Mo in rock chips from leached alteration zone
• Drilling aims to vector follow-up drilling toward potential potassic copper-rich porphyry zones
• No evidence of historical drilling at Piedras Blancas
• GSC holds the rights to own 100% of the Piedras Blancas prospect

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "We are very excited to start our new drilling campaign at Piedras Blancas as it represents the Company's first drill test of a porphyry copper target at Especularita.

"An initial three scout RC holes are planned, which will test a window of outcropping porphyry-style alteration enclosed by gravels and scree. The alteration is characteristic of the phyllic zone of porphyry copper systems with pervasive silica-sericite-pyrite overprinted by stockworks of pyrite and quartz-pyrite fracture veins. The surface geology is highly oxidised and leached, so we want to get below the oxide zone and confirm what's there and use that information to potentially vector toward the potassic copper-rich core of the porphyry system."

Piedras Blancas Porphyry Cu Prospect:

Piedras Blancas is located at the northwestern margin of the La Colorada lithocap that comprises the Company's principal porphyry copper target within its flagship Especularita project (Figure 1). The Especularita project is located 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).

Scout RC Drilling Programme:

Scout RC drilling has commenced at Piedras Blancas (White Stones), where the overlying La Colorada lithocap is interpreted to have been eroded away, exposing possible porphyry-style phyllic alteration comprising intense quartz-sericite-pyrite overprinted by stockworks and crackle veinlets of quartz-pyrite mineralisation (Figure 2). Intense weathering and oxidation of the surface rocks have resulted in depleted (leached) copper signatures for rock chip samples in the area. However, molybdenum, which is a useful pathfinder element for porphyry copper mineralisation, is less mobile in the oxide environment and exhibits strong anomalism with assay results up to 49ppm Mo from 13 rock samples of the alteration zone.

The drilling target is further defined by a prominent broad zone of de-magnetisation in the drone magnetics survey1 which is a feature consistent with pervasive magnetite-destructive phyllic alteration in porphyry copper settings. On a local prospect scale, however, subtle magnetic features are evident which will be tested with this drilling programme (Figure 3).

An initial test of three scout RC drill holes (Figure 3) has been designed with the aim of determining the depth of oxidation and leaching and confirming that the alteration observed in outcrop corresponds at depth to the phyllic zone of a porphyry copper system. The inner phyllic zone, or "shell", may host lower grade copper mineralisation, however, the results for this drilling are aimed to provide strong vector indicators for possible follow-up drilling targeting the potassic core of the porphyry system which typically comprises higher copper grades and may be located at depth or laterally beneath the gravel cover (or both).

Figure 2: Oxidised quartz-sericite-pyrite (QSP) alteration overprinted by quartz-pyrite stockwork veining exposed in outcrop at Piedras Blancas ("White Stones") prospect, Especularita. Alteration is characteristic of the phyllic alteration zone in porphyry copper systems.

Next Steps:

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

Final results for Phase III diamond drilling at Mostaza are still awaited, as are results for metallurgical testwork 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 prospect. New results from this ongoing work, together with results of the recent ground magnetic survey, will direct targeting for the next phase of drilling at Viuda.

Figure 3: Preliminary plan for scout RC drilling at Piedras Blancas illustrating geology (left) and Vertical Signal Magnetic Intensity (right).

References:

• RNS 7231B (06 June 2023): Magnetic survey commences at Especularita.

Forward Looking and Cautionary Statements