Drilling Completed at Viuda Negra Prospect

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21 May 2025

Great Southern Copper plc

("GSC" or the "Company")

Drilling Completed at Viuda Negra Prospect Targeting Outcropping Gold-Silver Mineralisation

Exploration update, Especularita Project

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold exploration in Chile, is pleased to provide an update on exploration activity across its Especularita Project, where its scout diamond drilling programme targeting gold-silver mineralisation at the Viuda Negra prospect is complete.

Highlights:

· Scout diamond drilling at Viuda Negra completed with four holes drilled for a total of 553.05 m

· Drilling targeted outcropping Maricunga-style vein alteration with gold grades in rock chip and channel samples up to 4.2g/t Au and 145g/t Ag

· All holes intersected broad zones of quartz-magnetite vein alteration and breccia

· At Mostaza, core samples for Phase II drill holes CNG25-DD011 to DD017 have been dispatched to ALS Laboratories with the remaining holes due to be sampled before the end of May

· Planning and permitting for geophysics surveys and Phase III drilling at Mostaza, Cerro Negro is in progress

· Reconnaissance exploration has commenced at Brechia Amarilla prospect with rock chip samples of outcropping mineralisation grading up to 1.8% Cu and 2.12g/t Au

· GSC holds options to 100% of the prospects that make up its Especularita Project

· Excellent access to nation infrastructure including roads, power, port and townships

Sam Garrett, CEO for Great Southern Copper in Chile, said: "We are extremely pleased with the progress of the scout diamond drilling at Viuda Negra which targeted anomalous gold and silver results from outcrops of Maricunga-style alteration. All holes intersected the target alteration system comprising broad zones of quartz-magnetite banded veining and breccia hosted in feldspar porphyry.

"Processing of core samples for the Phase II drilling at Mostaza is continuing with samples for the first seven holes now at the ALS laboratory. Work is ongoing to deliver all samples for the final Phase II drill holes to the laboratory before the end of this month. Planning and permitting for geophysics surveys and Phase III drilling at Cerro Negro is in progress.

"Meanwhile, exploration across the broader Especularita Project portfolio continues with reconnaissance mapping and sampling commencing at the Brechia Amarilla prospect where strongly anomalous copper and gold results, up to 1.8% Cu and 2.12g/t Au in rock chip samples, are indicative of the potential for intrusive-related style copper-gold mineralisation."

The Company provides an exploration update for the Viuda Negra, Mostaza and Brechia Amarilla prospects which are all located within GSC's Especularita Project in northern Chile (Figure 1).

Figure 1: GSC's Especularita Project, Chile highlighting location of Cerro Negro, Viuda and Brechia Amarilla prospects.

Viuda Negra prospect scout diamond drilling:

The Company's scout diamond drilling programme at Viuda Negra prospect has been completed with four holes drilled for a total of 553.05 m. Drilling targeted anomalous Au-Ag-Cu assay results in rock chip and channel samples (Figure 2) grading up to 4.2g/t Au, 145g/t Ag and 0.56% Cu associated with a northwest-trending zone of silicification and Maricunga-style banded quartz-magnetite veinlet alteration1.

Drill holes VNE25-DD001 to DD003 targeted the outcropping alteration zone over 250m of strike, whereas hole DD004 was drilled below and to the southeast of hole DD002 to test depth continuity of the alteration intersected in that hole. All holes intersected broad zones of the vein alteration system comprising banded quartz-magnetite veining and quartz-filled crackle breccia (Figure 3). Vein density of the banded veinlet alteration in drill core averages >10-20 veins/m ranging locally up to >50 veins/m.

The vein alteration system is dominantly hosted within and marginal to a swarm of intermediate argillic altered feldspar porphyry dykes intruding magnetite-albite-chlorite altered microdiorite.

Figure 2: Drilling plan for Viuda Negra prospect with rock chip geochemistry, Especularita. Drilling targeted outcropping "Maricunga-style" banded quartz-magnetite vein alteration (right) with anomalous gold and silver geochemistry.

Figure 3: Vein alteration textures observed in drill core at Viuda Negra prospect, Especularita. Veinlet and breccia-hosted mineralisation in drillhole VNE25-DD001 (above). Sheeted Maricunga-style banded quartz+pyrite veinlets (bottom-left) and stockwork quartz-pyrite and banded veinlets cut by quartz-calcite-chalcopyrite veins (bottom-right), 63-82m VNE-DD002.

Mostaza Phase II drilling, Cerro Negro:

Core samples for Phase II drill holes CNG25-DD011 to 017 at Mostaza have been dispatched to ALS Laboratories in Santiago. Results are pending.

Geological and geotechnical surveys and sampling of the remaining holes is on-going with all samples aimed to be despatched to the laboratory before the end of the month.

Brechia Amarilla reconnaissance exploration:

Reconnaissance mapping and sampling at the Bechia Amarilla (Yellow Breccia) prospect, located at the northwestern margin of the Especularita Project (Figure 1), has identified outcropping intrusive-related copper-gold mineralisation associated with an ovoid-shaped (400x400m) granodiorite body intruding into propylitic altered (epidote-chlorite) dioritic host rock.

The mineralised granodiorite is strongly altered to silica-albite and appears to be structurally emplaced along an arcuate northwest-trending fault (Figure 4). Small-scale artisanal mining is prevalent throughout the granodiorite exposing strong oxide copper mineralisation on fracture surfaces (Figure 5a). Elsewhere, sulphide copper (chalcopyrite-bornite) occurs typically as coarse disseminations and blebby in-fillings of myriolitic cavities (Figure 5b), which characterises the mineralisation as a potentially intrusive-related copper-gold system.

A total of 17 reconnaissance rock grab samples were collected across the concession area although dominantly within the mineralised granodiorite. Thirteen samples (76.5%) were highly anomalous in copper (>500ppm Cu) ranging to a peak assay grade of 1.8% Cu. Two samples (11.8%) assayed grades over 1% Cu. Six samples (35.3%) were highly anomalous in gold (>0.1g/t Au) with a peak assay grade of 2.12g/t Au.

Detailed prospect-scale mapping and sampling is continuing at Bechia Amarilla.

Figure 4: Reconnaissance geology and copper geochemistry map for the Brechia Amarilla prospect, Especularita.

Figure 5: Oxide copper mineralisation in surface outcrops at Brechia Amarilla (l), and coarse blebby disseminated sulphide copper in-filling myriolitic cavities in granodiorite (r).

References:

1. RNS 2553F (16 April 2025); Scout RC drilling at Viuda confirms potential for mineralised porphyry Au-Ag-Cu deposit.

Enquiries:

Notes for Editors:

About Great Southern Copper

Great Southern Copper PLC is a UK-listed mineral exploration company focused on the discovery of copper-gold deposits in Chile. The Company has the option to acquire rights to 100% of two projects in the under-explored coastal belt of Chile that are prospective for large scale copper-gold deposits. Chile is a globally significant mining jurisdiction being the world's largest producer and exporter of copper.

The two, early-stage Cu-Au projects comprise Especularita and San Lorenzo Projects, both located in the coastal metallogenic belt of Chile which hosts significant copper mines and deposits, including Teck's Carmen de Andacollo copper mine, and boasts excellent access to infrastructure such as roads, power and ports. Significant historical small-scale and artisanal workings for both copper and gold are readily evident in both exploration project areas. The coastal belt offers deposit type optionality for copper including porphyry and IOCG style deposits as well as newly recognised intrusive-related copper and gold deposits.

Great Southern Copper is strategically positioned to support the global market for copper - a critical battery metal in the clean energy transition around the world. The Company is actively engaged in exploration and evaluation work programmes targeting both large tonnage, low to medium grade Cu-Au as well as high-grade Cu-Ag-Au deposits.

Further information on the Company is available on the Company's website: https://gscplc.com

Competent Person Statement

The information in this announcement that relates to exploration results is based on and fairly represents information reviewed or compiled by Mr Sam Garrett, a Competent Person who is a Member of the Australian Institute of Geoscientists and a Fellow of the Society of Economic Geologists. Mr Garrett is the CEO and a shareholder of Great Southern Copper PLC. Mr Garrett has sufficient experience that is relevant to the styles of mineralisation and types of deposit under consideration and to the activity being undertaken to qualify as a Competent Person as defined in the 2012 Edition of the "Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves". Mr Garrett has provided his prior written consent to the inclusion in this announcement of the matters based on information in the form and context in which it appears.

This announcement includes information that relates to Exploration Results prepared and first disclosed under the JORC Code (2012) and extracted from the Company's previous LSE announcements as noted, and the Company's Prospectus dated 20 December 2021. Copies of these announcements are available from the LSE Announcements page of the Company's website: www.gscplc.com.

The Company confirms that it is not aware of any new information or data that materially affects the information included within the Prospectus dated 20 December 2021.

Forward Looking and Cautionary Statements

Some statements in this announcement regarding estimates or future events are forward-looking statements. They include indications of, and guidance on, future earnings, cash flow, costs and financial performance. Forward-looking statements include, but are not limited to, statements preceded by words such as "planned", "expected", "projected", "estimated", "may", "scheduled", "intends", "anticipates", "believes", "potential", "predict", "foresee", "proposed", "aim", "target", "opportunity", "could", "nominal", "conceptual" and similar expressions. Forward-looking statements, opinions and estimates included in this report are based on assumptions and contingencies which are subject to change without notice, as are statements about market and industry trends, which are based on interpretations of current market conditions. Forward-looking statements are provided as a general guide only and should not be relied on as a guarantee of future performance. Forward-looking statements may be affected by a range of variables that could cause actual results to differ from estimated or anticipated results and may cause the Company's actual performance and financial results in future periods to materially differ from any projections of future performance or results expressed or implied by such forward-looking statements. So, there can be no assurance that actual outcomes will not materially differ from these forward-looking statements.