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.

18 December 2025

Great Southern Copper plc

("GSC" or the "Company")

Ground Magnetics Survey Commences at Viuda Gold Prospect

Targeting Maricunga-style porphyry Au-Cu 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 a ground magnetic survey at its Viuda porphyry Au-Cu prospect ("Viuda") at the Company's Especularita project.

Highlights:

·      Ground magnetics commences with a 250 line-kilometre survey at Viuda

·      Exploration targeting large-scale Maricunga porphyry Au-Cu type deposits

·      Previous scout drilling intersected broad zones of gold mineralisation, including¹;

o  DD004: 6.7m @ 0.39 g/t Au & 0.12% Cu from 43.1m, within broader interval of:

§ 121.5m @ 0.11 g/t Au & 0.05% Cu from 6.5m, and

o  DD002: 14.2m @ 0.21 g/t Au & 0.11% Cu from 11m, within broader interval of:

§ 73m @ 0.14 g/t Au & 0.1% Cu from 11m

·      High gold grades hosted in stockwork veining within magnetic porphyry intrusive

·      Phase II drilling at Viuda is anticipated in early 2026

·      GSC has option to earn 100% of the Viuda prospect

·      Viuda located at low elevation with excellent access to infrastructure and mining services

Porphyry Au deposits in Chile:

Scout drilling by GSC at Viuda earlier this year confirmed that gold and copper mineralisation is associated with stockwork and sheeted dark-banded and A-type quartz veinlets within widespread intermediate-argillic and magnetite-albite-chlorite altered diorite porphyry intrusives. The mineralisation and alteration are typical of Maricunga-style gold porphyry systems, such as Kinross Gold's Lobo-Marte deposit (6.7Moz Au at 1.3 g/t²), Maricunga (4.3 Moz at 0.7 g/t³) and Rio2's Fenix deposit (1.77 Moz Au at 0.48 g/t Au⁴).

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Previous work by the company, including drilling, has established mineralisation and alteration at Viuda that are consistent with a Maricunga-style porphyry gold system, a style which has not previously been reported within the coastal metallogenic belt of Chile. In particular, scout drilling has demonstrated that higher grades of gold are associated with a magnetic porphyry intrusive.

"This ground magnetics survey is planned to identify potential magnetic intrusives that will assist the company in vectoring its next phase of drilling at Viuda, which is anticipated to commence within the first quarter of 2026. I look forward to keeping shareholders and the wider market informed as exploration at Viuda progresses and as results from the ground magnetic survey are received and interpreted."

Viuda Prospect:

The Viuda and Viuda Negra prospects, located approximately 15km to the southwest of the Company's Cerro Negro, comprises 18km² of concessions centred upon a prominent hill of resistive silicified rock (Chingay Hill) and surrounded by a 2km wide bowl-shaped depression ("bajo") of dominantly albite-pyrite-clay altered volcanics and intrusive rocks - a geological setting typical of many porphyry deposits, formed by supergene weathering and oxidation.

Viuda Negra is located approximately 1km to the east of Chingay Hill, and recent scout drilling intersected broad intervals of anomalous gold including¹;

·    DD004: 6.7m @ 0.39 g/t Au & 0.12% Cu from 43.1m, within broader interval of:

o  121.5m @ 0.11 g/t Au & 0.05% Cu from 6.5m

The discrete higher-grade interval in DD004 is associated with a porphyritic microdiorite intrusive phase which is over-printed by abundant banded and A-type quartz veinlets and intense, magnetite-rich potassic alteration. This is interpreted as an early-mineral porphyry phase and suggests that higher-grade centres may be present elsewhere within the system.

Ground magnetics survey:

The Viuda ground magnetics survey comprises a 250 line-kilometre survey with east-west orientated grid-lines and a line spacing of 50m (Figure 1). The survey is being completed by Santiago-based Southern Geophysics and covers the full extent of the clay-altered "bajo" which defines the prospect.

The survey is designed to identify potassic-altered magnetic intrusive bodies that are potentially indicative of porphyry Au-Cu mineralisation as identified in hole DD004 of the scout drilling programme.

Figure 1: Oblique Google image of the Viuda and Viuda Negra prospect illustrating grid lines of the ground magnetics survey.

  References:

1.    RNS 4145X (01 September 2025): Results of scout drilling at Viuda Negra

2.    Kinross Gold 2024 Annual Mineral Resource and Resource Statement

3.    Kinross Gold 2015 Annual Mineral Resource and Resource Statement

4.    NI 43-101 Technical Report on the Feasibility Study for the Fenix Gold Project

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-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.