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.

13 April 2026

Great Southern Copper plc

("GSC" or the "Company")

GSC Expands Footprint at La Colorada Lithocap Porphyry Cu-Au Prospect with New Concessions

Dominant position strengthened over highly prospective and under-explored target

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that it has increased its concession footprint at the La Colorada Lithocap prospect, part of the Especularita Project, which is highly prospective for porphyry Cu-Au type deposits.

Highlights:

·    GSC expands footprint at La Colorada with five new concessions totalling 1000 hectares ("ha"), securing control over the central core of a large-scale lithocap alteration system

·    Dominant land position further enhanced over a highly prospective and under-explored porphyry Cu-Au target

·    La Colorada is defined by an over 75km² high-sulphidation lithocap - a scale capable of hosting multiple porphyry systems

·   Located on a major mineralised trend alongside world-class porphyry deposits including Los Pelambres, Altar and El Pachon

·   Exploration programmes underway with mapping, sampling and geophysics designed to vector toward potential porphyry centres at depth

·    Clear pathway towards scout RC drilling, with targeting, planning and permitting well advanced

·    Company holds rights to 100% of the Especularita Project which includes the La Colorada prospect

·    The Especularita Project is located in Chile's coastal metallogenic belt with excellent access to infrastructure and mining support services

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Advanced argillic high-sulphidation lithocaps are well known to occur above porphyry copper and copper-gold deposits globally, and GSC's La Colorada prospect is a giant example with the alteration system extending for over 75 square kilometres in area. Significantly, La Colorada sits within a lineament that hosts massive porphyry copper-gold deposits, including Los Pelambres, Altar, Piuquenes and El Pachon, and yet remains relatively unexplored.

"GSC's new concessions, totalling 1,000 hectares, significantly strengthens our already dominant position over the lithocap and, critically, secures control of the central core of the alteration system for the Company.

"Exploration, including mapping, sampling and geophysics, is planned to systemically vector towards potential porphyry copper centres at depth. In parallel, planning and permitting for scout RC drilling targeting the western and southern margins of the lithocap are well advanced, and we hope to commence these programmes within the month."

La Colorada Porphyry Cu-Au Prospect:

Great Southern Copper's Especularita Project is centred around the giant La Colorada lithocap located within the Cretaceous-age coastal metallogenic belt of northern Chile. The prospect is defined by its distinctive high-sulphidation style alteration blanket mapped over an area greater than 75 km² within a northwest-southeast trending structural lineament that links the prospect with notable porphyry Cu-Au mines and projects (Table 1) including Los Pelambres mine, Altar and El Pachon (Figure 1). To the north the prospect is on trend of the Carmen de Andacollo porphyry copper (Teck) and gold mines (Galantas) which, significantly, are developed beneath an advanced argillic lithocap of similar type and dimension to La Colorada and hosted in similar aged rocks at similar elevation.

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.

Regional mapping at Especularita suggests that the La Colorada alteration system is controlled locally by the dominant northwest-southeast trending Victoria Fault and is off-set by regular late northeast-trending structures. The Cerro Negro high-grade Cu-Ag deposit is located within a southeastern dislocated section of the lithocap (Figure 1).

The new concessions further strengthen the Company's control over this highly prospective alteration system and are considered critical as they potentially occupy the central core to the mineralising system where alteration may be the most intense (hottest and most acidic).

Table 1: Resource information for deposits located along trend of GSC's Especularita project, Chile. *CuEq grade Cu-Au-Mo

Figure 2: La Colorada lithocap in background (looking to the southeast from Artemisa Prospect) with clay-rich argillic alteration clearly visible and phyllic type alteration underlying in the foreground being investigated by GSC geologists. The lithocap includes classic alteration textures, including (l to r) advanced argillic vughy silica, argillic clay alteration, intense pyrite alteration (oxidised) and brecciation.

Lithocaps and Porphyry Cu-Au Mineralisation:

Advanced argillic high-sulphidation lithocaps are well known to occur above porphyry copper and copper-gold deposits globally although are not widely observed above deposits in Chile due to the actions of rapid tectonic uplift and erosion. Notable exceptions include Carmen de Andacollo and Valeriano-El Encierro (Figure 3).

Generally, lithocaps comprise subsurface, broadly stratabound alteration domains that are laterally and vertically extensive with lateral dimensions greater than 10 km and thicknesses of more than 1 km, hence they are often referred to as "blankets". They typically form when acidic magmatic-hydrothermal fluids rising off a porphyry intrusive at depth react with wallrocks during ascent towards the paleosurface. Although lithocaps typically have steeply-dipping structural roots, there is a significant component of lateral fluid flow involved in their formation, either through permeable aquifers and/or a well-developed lateral fracture system.

Although lithocaps are commonly barren, high sulfidation Au-Ag-Cu mineralisation typically occurs in silicic altered rocks, either as stratabound replacements, veins and/or breccia cement. The silica-clay-rich alteration assemblages are invariably magnetite-destructive and can obscure the magnetic signature of an underlying porphyry deposit. Pyrite alteration is ubiquitous in lithocaps and mapping pyrite concentration can be an important vector indicator. Supergene weathering of pyrite (interaction with surface water) produces H₂SO_4, creating highly acidic fluid conditions which acts to leach the lithocap of minerals and metals, creating the distinctive and characteristic vughy silica texture (and may also produce supergene enrichment blankets at depth).

Where present, the broad, flat-lying and chemical inert nature of the lithocap acts to mask (or blanket) the location of porphyry copper deposits below. Explorers need to rely on other tools, such as geophysics and clay mineralogy, to attempt to identify the higher temperature and more acidic parts of the lithocap that sit above the feeder zones leading to the potassic-altered core of the porphyry mineralising system at depth (Figure 4). The lithocap may mask multiple porphyry copper deposits and the buried porphyry copper deposit may not necessarily be centrally located beneath the lithocap, highlighting the importance of understanding the lithocap geology and geochemistry (vectoring).

Figure 3: Scale comparison of Chilean porphyry copper lithocap relative to GSC's untested La Colorada lithocap at Especularita.

Figure 4: Model for porphyry copper deposits below lithocaps.

Next Steps:

Ground exploration covering the five new concession blocks will be incorporated into the broader ongoing La Colorada exploration programme including mapping and sampling. Spectral mapping of alteration minerals will be key to vectoring toward hot, acidic feeder zones. Geophysics surveys (AMT and magnetics) are also planned to commence this quarter.

References:

1.    2025 Annual Report and Financial Statements Antofagasta PLC

2.     2016 Portergeo Report on Carmen de Andacollo, https://portergeo.com.au/database/mineinfo.php?mineid=mn112

3.    2024 Mineral Resource Estimate Aldebaran Resources

4.    2025 Glencore market release 18Aug2025

5.    2026 Corporate presentation McEwen Mining Inc.

6.    2025 ASX Announcement Southern Hemisphere 30Jul2025

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/

Enquiries:

Subscribe to our news alert service: https://gscplc.com/auth/signup

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.