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.

21 May 2026

Great Southern Copper plc

("GSC" or the "Company")

Geophysics AMT Survey Commences at La Colorada Lithocap, Especularita

Survey to target large-scale buried porphyry copper deposits

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that it has commenced an audio-frequency magneto-telluric ("AMT") geophysics survey across the La Colorada lithocap prospect at its Especularita Project.

Highlights:

·    Survey to cover an area of approximately 33 km² comprising western half of the La Colorada lithocap

·    Targeting large-scale porphyry copper deposits at depth below the high sulphidation lithocap

·    Survey to be completed in two weeks with results expected within 4-6 weeks

·    Results to assist with target vectoring for first-pass scout drilling of the lithocap

·    GSC holds rights to own 100% of the Especularita Project

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

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "The AMT geophysics survey is designed to allow us to see through the lithocap blanket that masks potential porphyry copper deposits at depth. Used in conjunction with ongoing soil geochemistry and spectral rock studies, the survey will help refine and prioritise targets for first-pass scout drilling across the lithocap, which we expect to commence early in the second half of this year.

"The AMT technique is ideally suited for mapping deeply buried porphyry copper deposits because it effectively penetrates thick, conductive cover (such as volcanic lithocaps) to delineate both the deep, localised resistive intrusions and the conductive alteration halos characteristic of porphyry systems.

"Meanwhile, scout RC drilling is continuing at the Artemisa North target, while preparation work is advancing at both the Viuda and Cerro Negro prospects as we progress exploration across multiple targets at Especularita."

La Colorada Lithocap Porphyry Copper Targets:

The La Colorada lithocap comprises the cornerstone of the Company's flagship Especularita project located 100 km south of the port of Coquimbo (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 50 million tonnes of contained copper metal defined in mines and advanced projects.

Audio-Frequency Magneto-Telluric Survey:

The Company has contracted Chile-based Southernrock Geophysics S.A. to undertake an AMT survey covering an area of approximately 33 km² and comprising the western half of the La Colorada lithocap (Figure 2). The survey is planned on 500 metres ("m") grid centres and is designed to identify potential large-scale porphyry copper centres hidden at depth beneath the high-sulphidation alteration blanket. The survey parameters allow for the depth of investigation to exceed 1000m below surface, subject to the resistivity nature of the rock.

Figure 2: Approximate AMT survey area for the La Colorada lithocap, Especularita. Field team measuring EM activity on site at La Colorada - note the highly oxidised and clay-rich lithocap rocks in the background.

Audio-frequency magneto-tellurics (AMT) is a passive electromagnetic geophysical technique ideally suited for mapping deeply buried porphyry copper deposits as it effectively penetrates thick, conductive cover (such as volcanic lithocaps) to delineate the deep, localized resistive intrusions and conductive alteration halos characteristic of porphyry systems. The method measures natural electromagnetic (EM) fields on the Earth's surface generated from lighting (high frequency) and solar winds (low frequency) to map subsurface electrical resistivity. By analyzing how these waves interact with different rock types, geophysicists can interpret geological units, fault zones, and potential mineral deposits down to depths of up to a few kilometers.

Porphyry copper deposits may have distinct three-dimensional electrical signatures. When integrated through 3D inversion modelling, AMT maps these contrasts at depths ranging from 100 meters to over 2 kilometers. The causative porphyry intrusions typically appear as highly resistive bodies whereas the highly mineralized potassic cores and surrounding phyllic (pyrite-rich) and argillic alteration zones form conductive anomalies due to interconnected sulfide minerals and clay alteration.

Next Steps:

Scout RC drilling is currently in progress at the Artemisa North target with 3 holes completed for 414m. The fourth hole ART26-RC008 is currently in progress at a depth of 220m. Samples for holes ART26-RC005 and RC006 have been delivered to ALS Laboratories in Santiago by GSC personnel. Once completed at Artemisa North, the scout RC drilling programme will progress to test the Artemisa South and Victoria targets.

Exploration work, including mapping and sampling, is in progress at both the Cerro Negro and Viuda prospects in preparation for drilling. Metallurgical studies are also underway for Mostaza core samples from Phases I and II of the drilling at Cerro Negro.

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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.