Exploration Results Extend Cerro Negro

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold exploration in Chile, is pleased to report the results of exploration sampling and mapping at Cerro Negro, along trend to the south of the previously reported high-grade drill results at Mostaza mine.

Highlights:

• Assay results for exploration channel chip samples range up to 0.93% Cu and 86.4 g/t Ag
• Newly discovered outcropping mineralised breccias including artisanal mine workings extend mineralisation 2 km south of high-grade Cu-Ag Phase I drill intercepts including1,2;

o CNG25-DD001: 20m @ 3.3% Cu and 270 g/t Ag from 27m

o CNG25-DD007: 33m @ 1.96% Cu and 60.6 g/t Ag from 87m

• Mineralisation remains open further to the south
• Phase II drilling at Mostaza completed with 16 holes drilled for a total of 1,701m
• Detailed surface exploration will continue to define Phase III exploration drill targets
• GSC holds option to 100% ownership of the Cerro Negro prospect including Mostaza mine
• Excellent access to national infrastructure including roads, power, towns and ports

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "These results are very significant demonstrating that the structural trend which hosts the high-grade copper-silver mineralisation at Mostaza continues for a further two km along strike to the south of the mine.

"Mineralisation is open to the south and our ground exploration efforts will continue in earnest with the aim to further extend the mineralised trend and define drill targets for the Phase III exploration drilling programme.

"Meanwhile, deposit modelling and metallurgical test work on the Mostaza drill core has commenced and scout diamond drilling continues at our Viuda Negra prospect targeting porphyry-epithermal style Au-Ag-Cu mineralisation.

"This is an exciting time for GSC with multiple drill programmes progressing across multiple prospects at our Especularita project and we look forward to updating the market with new results."

Results of Surface Mapping and Sampling

59 rock chip and channel chip samples were collected during prospect-scale mapping and sampling programmes at Cerro Negro. The exploration programme was designed to identify potential for extensions of high-grade Cu-Ag mineralisation to the south of the Mostaza mine workings. This work supplements the previously collected 162 samples which returned assays up to 4.64% Cu and 177ppm Ag3 (reported 31 October 2024).

Samples were collected along a trend of outcropping mineralised lenses extending 2km south of the Mostaza Mine (Figure 1). The anomalous rock chip geochemistry defines an approximately 300m wide, north-south trending structurally controlled corridor (the Mostaza Fault zone) defined by intensely leached and oxidised silica alteration and artisanal mine workings including a new zone of mineralised magnetite-quartz rich breccia discovered 800m south of previous mapping (Figure 2).

Assay results for the 59 new samples have been received with copper grades ranging up to 0.93% Cu with 12% of samples assaying >0.1% Cu, many of which are concentrated in the southern-most zone coinciding with the new lens discovery. Silver assay grades range up to 86.4 g/t Ag with 20% of samples assaying >10 g/t Ag. The mineralised lenses are typically depleted in both Cu (<100ppm) and Ag at surface due to weathering and oxidation. Based on drilling results to date, higher grades might be expected at depth beneath these surface exploration results.

In addition to anomalous Cu and Ag, samples within the mapped lenses are highly anomalous in As-Sb-Ba ± Mo-Bi-Te-Pb-Zn. This geochemical association is the same as observed in the high-grade drill intercepts, confirming potential for high-grade mineralisation within the southern extension zone.

Sampling and Assaying:

All rock samples collected are located using hand-held GPS units (WGS84 zone 19S datum, UTM coordinate system) and allocated a unique sample number using a ticket-book system.

Figure 1: New and previously reported Cu (left) and Ag (right) assay results in rock and channel chip samples at Cerro Negro prospect, Especularita. Note high values associated with newly discovered lens 800m to the south of previous mapping, and 2,000 south of the Mostaza mine.

Figure 2: Cut sample (left) and outcrop (right) of magnetite-quartz-sulphide infilled breccia. Newly discovered mineralised zone.

Phase II Drilling

Phase II diamond drilling at Mostaza has been completed, with 16 holes drilled for a total of 1,701.7m (Figure 3). The program targeted depth extensions of the high-grade mineralisation identified beneath the Mostaza pit in Phase I, to a vertical depth of 100m below the original hole CNG25-DD001 intercept. Additionally, several drillholes targeted extensions to the north (Lens 1) and south (Lens 4) of the Mostaza Mine. The drillholes are currently being sampled and assayed.

Figure 3: Cerro Negro Project, Mostaza Mine. Map showing location of Phase I and Phase II GSC drillholes and surface mapped mineralised Lenses.

About the the Mostaza Cu-Ag deposit, Cerro Negro

High-grade Cu-Ag mineralisation at Mostaza is confined to a north-south trending, structurally controlled lode, or "lens" (specifically Lens 2), of variable width (<4-20m) that dips moderately steeply to the west. Copper-silver mineralisation comprises abundant disseminations, veinlets, crackle networks and breccia matrix fillings of hypogene black to dark metallic grey chalcocite with lesser bluish bornite and traces of chalcopyrite and pyrite.

Host rocks to mineralisation comprise multiple generations of intensely altered breccia, tuffisite and felsic intrusive. The mineralised lens is bound to the east and west by faults that are typically invaded by narrow (1-2m) andesite to rhyolite dykes. Outside of the bounding dykes and faults, the enclosing wall rocks consist of an east-dipping bedded sequence of fresh, black volcanic lava flows and brecciated dacite that might be part of a large dome-diatreme complex outcropping to the east.

The Lens 2 mineralisation is interpreted to form one of a number of Cu-Ag rich bodies mapped at surface which have historically been interpreted as discrete "lenses" but which collectively have the potential to make up an anastomosing network of structurally controlled zones of mineralisation continuous over a strike length of greater than 1-2km.

References:

• RNS 5182Y (26 Feb 2025): Cerro Negro assays return 20m of 3.3% Cu and 270g/t Ag
• RNS 8896D (07 Apr 2025): Further exceptional assays from Mostaza
• RNS 3120K (31 Oct 2024): Cerro Negro results up to 4.64% Cu and 177g/t Ag

Forward Looking and Cautionary Statements