THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION AS STIPULATED UNDER THE UK VERSION OF THE MARKET ABUSE REGULATION NO 596/2014 WHICH IS PART OF ENGLISH LAW BY VIRTUE OF THE EUROPEAN (WITHDRAWAL) ACT 2018, AS AMENDED.  ON PUBLICATION OF THIS ANNOUNCEMENT VIA A REGULATORY INFORMATION SERVICE, THIS INFORMATION IS CONSIDERED TO BE IN THE PUBLIC DOMAIN.

02 June 2026

Great Southern Copper plc

("GSC" or the "Company")

Scout RC Drilling Commences at Victoria Porphyry Copper Target

Drilling to also test high-grade breccia-vein and disseminated copper mineralisation

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 Victoria porphyry copper target at the Especularita Project, while drilling recently completed at the nearby Artemisa North target has confirmed evidence of a strong porphyry copper-style alteration system.

Highlights:

Victoria

·    Scout reverse circulation ("RC") drilling commences at Victoria porphyry copper prospect, located at the southern margin of the La Colorada lithocap

·    Four holes planned to test high-grade vein and disseminated type mineralisation identified in outcrop

·    Drilling to test beneath artisanal and small-scale workings

·    Rock chip geochemistry results grade up to 6.9% Cu, 1.85g/t Au and 84.8g/t Ag¹

·    Large-footprint system open under shallow gravel-scree cover

·    No previous drilling of the target

·    GSC holds rights to own 100% of the Victoria target

·    Prospect located at low elevation with excellent access to infrastructure and mining services and along trend of major copper deposits including Los Pelambres, Altar and El Pachon.

Artemisa North

·    Scout RC drilling completed at Artemisa North prospect with five holes drilled for 796 metres ("m")

·    All holes successfully intersected biotite-chlorite-magnetite alteration with variable sulphide mineralisation

·    Style and intensity of alteration provide proof-of-concept confirmation of a porphyry copper type setting at Artemisa North intersected at shallower depths than expected and further increasing prospectivity of the broader La Colorada lithocap

·    Samples for the first four holes at Artemisa North have been despatched to ALS Laboratories in Santiago

·    GSC holds rights to own 100% of the Artemisa North target

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Victoria is the third of four targets to be tested with scout RC drilling in the current porphyry exploration programme. This programme is focusing on targets on the western and southern margins of the La Colorada lithocap that display geological, geochemical and spectral features that are characteristic of porphyry copper systems. Drilling will also test beneath high-grade copper-gold-silver mineralisation identified in old workings, providing an opportunity to assess both the broader porphyry potential and the higher-grade mineralised structures observed at Victoria.

"The drilling programme is progressing well with both the Piedras Blancas and Artemisa North programmes now successfully completed. Combined with the encouraging geological observations from Piedras Blancas, these results continue to strengthen our confidence in the broader prospectivity of the La Colorada lithocap to host a significant porphyry copper system. We look forward to receiving and reporting assay results in due course.

"Meanwhile, the AMT geophysics survey is in progress across the western half of the lithocap and exploration mapping and sampling activities are continuing at both the Cerro Negro and Viuda prospects as we prepare for the next phase of drilling activity in those areas."

Victoria Porphyry and Breccia-Vein Target:

The Victoria prospect is located 2.5km southeast of the Artemisa North drilling target along the southern margin 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 50Mt of contained copper metal defined in mines and advanced projects.

Whilst much of the Victoria prospect area is covered by shallow gravel and scree deposits, mapping and sampling demonstrate that the target area encompasses a complex geologic intersection where the La Colorada lithocap is in structural contact with the Quilitapia batholith and the overlying andesitic volcanics separated by the regionally-extensive southeast-trending Victoria Fault (Figure 2).

To the south of the Victoria Fault high-grade copper-gold-silver mineralisation, grading up to 6.9% Cu, 1.84g/t Au, and 84.8g/t Ag¹ is associated with a set of north-south trending breccia-veins that are interpreted to extend out into the batholith and volcanics from the adjacent and overlying lithocap alteration. Float samples of the Victoria vein-breccias have previously reported gold grades up to 4.29g/t Au², indicative of a gold-rich system in contrast to the Mostaza style high-grade copper-silver mineralisation. Copper occurs typically as coarse, blebby disseminations of chalcopyrite and lesser bornite within the quartz breccia matrix (Figure 3).

In addition to the breccia-veins, high-grade copper at Victoria also occurs in quartz veinlets within steeply-dipping, structurally-controlled stockwork zones. High-grade disseminated copper is typically observed where these stockwork-mineralised structures interact with the hornfelsed andesitic volcanics. In this setting, the copper is recognised as black copper pitch or "wad" as fine disseminations or remobilised onto fracture planes (Figure 4).

The scout RC drilling programme at Victoria is planned to test both of these copper mineralisation styles.

 Figure 2: Geology and rock chip copper geochemistry map of the Victoria prospect illustrating location of proposed scout RC drill holes.

Figure 3: Outcrop of quartz-sulphide matrix vein breccia (l), coarse disseminated chalcopyrite hosted in quartz matrix breccia.

Figure 4: Green and black oxide copper mineralisation on fractures in hornfelsed andesitic volcanics from artisanal mine spoil.

Artemisa North Porphyry Target:

Drilling at the Artemisa North target has been completed with five scout RC holes drilled for a total of 796m. Samples for the first four holes, ART26 005 - 008 have been despatched to ALS Laboraties in Santiago.

Holes ART26 RC005, 006, 007 and 009 were drilled across a north-south trend of historical artisanal mine workings with abundant copper oxides and local specular hematite and quartz matrix breccias exposed at surface. All holes intersected dioritic rocks with pervasive chlorite-biotite-magnetite alteration with variable disseminated pyrite up to several percent and traces of chalcopyrite and quartz veins (Figure 5).

Hole ART26 RC008 was drilled to test a large zone of outcropping sericite alteration with quartz-limonite (after sulphide) veinlets and anomalous Mo in rock chip samples. The hole intersected strong chlorite-biotite-magnetite alteration in dioritic rocks, with widespread disseminated pyrite averaging several percent and locally over 20 percent. Traces of chalcopyrite and sphalerite and possible stockwork quartz veining are seen to increase generally down the hole (Figure 5).

These geological results are consistent with the potassic zone of porphyry copper systems, possibly developed in a precursor intrusive complex, and are potentially continuous with the potassic alteration intersected in the Piedras Blancas drilling to the north³, and further reaffirm our interpretation that we are testing the fringes of a large porphyry copper system which we believe underlies the extensive La Colorada lithocap to the east.

Scout RC Drill Programme and Sampling:

Scout RC drilling recently commenced at Victoria with a view to test the prospect for evidence of porphyry copper-gold and high-grade breccia-vein mineralisation and to provide vectors towards targets beneath the undrilled Colorada lithocap. A preliminary test comprising up to 1000m of drilling in at least four scout RC holes is now underway to assess the alteration and mineralisation.

The RC drilling method employed at Especularita collects samples on two-metre intervals. Representative samples for each sample of the cuttings are collected in large, individually numbered plastic bags, which are then weighed and transferred to a riffle splitter where they are separated (or split), and homogenised, three times into two duplicate samples of approximately 5kg each. GSC personnel then ticket and label one of the ±5kg samples using preprinted ticket books.

Finally, standard reference materials ("SRM's" or "Standards"), blanks, and duplicate samples are inserted into the sample sequence for the purpose of quality assurance / quality control ("QAQC"). The second ±5kg sample is used for geological description and stored for reference. An additional reference selection of cuttings for each two-metre sample is also retained in labelled boxes as a record of the geology of the drill hole.

At the completion of each hole, the representative 5kg samples are transported as a batch from the field and delivered by Company employees to ALS Laboratories in Santago or La Serena where they are prepared for analysis (weighed, dried, crushed and pulverised). A subsequent 200g split of each sample pulp is then forwarded to the ALS geochemical laboratory in Lima, Peru, where samples are assayed for gold (30g fire assay with ICP-AES finish, ALS code AU-ICP21) and 48 major, base and trace elements by ICP-MS following a four-acid digest (ALS code ME-MS61).

RC drilling was selected for this initial proof-of-concept stage as it is faster and cheaper than diamond drilling and allows for the rapid testing of more targets for the same cost.

Figure 5: Chip samples from Artemisa North drill holes (top row); Drillhole ART26 RC007, representative drill cuttings demonstrating chlorite-biotite-magnetite altered diorite with disseminated and veinlet pyrite±chalcopyrite at from left-to-right 56-58m,  120-122m, 134-136m, (bottom row); Drillhole ART26 RC008, representative drill cuttings demonstrating chlorite-biotite-magnetite altered diorite cut by veinlets of quartz-pyrite±chalcopyrite, and hairline veinlets of pyrite±chalcopyrite from left to right at 80-82m,  144-146m, 186-188m

Next Steps at Especularita:

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

Final results are awaited for the Mostaza metallurgical test work conducted on Phase I and II high-grade core samples. Planning and permitting for Phase IV drilling at Cerro Negro, including Mostaza, are in progress.

The AMT geophysics survey across the La Colorada lithocap is in progress. Planning for extensions to the Cerro Negro IP survey is also underway and anticipated to commence during June 2026.

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 Cerro Negro and Viuda.

References:

1.    RNS 0445B (03 April 2023): Rock Chip Assay Grades up to 6.9% Cu and 1.85g/t Au in Outcrop from Victoria Prospect

2.    RNS 2868U (27 March 2023): Float Sampling at Victoria Prospect Completed with Grades up to 2.1% Cu and 4.29g/t Au

3.    RNS 1366E (13 May 2026): Drilling commences at Artemisa North porphyry target

Engage with the GSC management team directly by asking questions, watching video summaries and seeing what other shareholders have to say. Navigate to our Interactive Investor hub here: https://gscplc.com/

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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-silver deposits in Chile. The Company has the option to acquire mining rights to 100% of Especularita project in the under-explored coastal belt of Chile that is prospective for large scale copper-gold-silver deposits. Chile is a globally significant mining jurisdiction being the world's largest producer and exporter of copper.

The Especularita Project is 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 the exploration project area. 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.